The only one that has any chance of sticking is the Possession of the weapon and him being under 18. There is even a problem with that charge as the law fucked up and had a subsection referring to people under the age of 16 which makes it ambiguous. A good lawyer(and he has a good lawyer) will probably even get him off on that.

Here is the law as written(and the sub section below referencing 16 years of age making the law ambiguous):

(1) In this section, “dangerous weapon” means any firearm, loaded or unloaded; any electric weapon, as defined in s. 941.295 (1c) (a); metallic knuckles or knuckles of any substance which could be put to the same use with the same or similar effect as metallic knuckles; a nunchaku or any similar weapon consisting of 2 sticks of wood, plastic or metal connected at one end by a length of rope, chain, wire or leather; a cestus or similar material weighted with metal or other substance and worn on the hand; a shuriken or any similar pointed star-like object intended to injure a person when thrown; or a manrikigusari or similar length of chain having weighted ends. (2)
(a) Any person under 18 years of age who possesses or goes armed with a dangerous weapon is guilty of a Class A misdemeanor. (b) Except as provided in par. (c), any person who intentionally sells, loans or gives a dangerous weapon to a person under 18 years of age is guilty of a Class I felony. (c) Whoever violates par. (b) is guilty of a Class H felony if the person under 18 years of age under par. (b) discharges the firearm and the discharge causes death to himself, herself or another. (d) A person under 17 years of age who has violated this subsection is subject to the provisions of ch. 938 unless jurisdiction is waived under s. 938.18 or the person is subject to the jurisdiction of a court of criminal jurisdiction under s. 938.183. (3)
(a) This section does not apply to a person under 18 years of age who possesses or is armed with a dangerous weapon when the dangerous weapon is being used in target practice under the supervision of an adult or in a course of instruction in the traditional and proper use of the dangerous weapon under the supervision of an adult. This section does not apply to an adult who transfers a dangerous weapon to a person under 18 years of age for use only in target practice under the adult’s supervision or in a course of instruction in the traditional and proper use of the dangerous weapon under the adult’s supervision. (b) This section does not apply to a person under 18 years of age who is a member of the armed forces or national guard and who possesses or is armed with a dangerous weapon in the line of duty. This section does not apply to an adult who is a member of the armed forces or national guard and who transfers a dangerous weapon to a person under 18 years of age in the line of duty. (c) This section applies only to a person under 18 years of age who possesses or is armed with a rifle or a shotgun if the person is in violation of s. 941.28 or is not in compliance with ss. 29.304 and 29.593. This section applies only to an adult who transfers a firearm to a person under 18 years of age if the person under 18 years of age is not in compliance with ss. 29.304 and 29.593 or to an adult who is in violation of s. 941.28.

Subsection 29.304:

(1) Persons under 12 years of age. (a) Prohibition on hunting. No person under 12 years of age may hunt with a firearm, bow and arrow, or crossbow. (b) Restrictions on possession or control of a firearm. No person under 12 years of age may have in his or her possession or control any firearm unless he or she is enrolled in the course of instruction under the hunter education program and he or she is carrying the firearm in a case and unloaded to or from that class under the supervision of his or her parent or guardian, or by a person at least 18 years of age who is designated by the parent or guardian, or is handling or operating the firearm during that class under the supervision of an instructor. (c) Restrictions on obtaining hunting approval. Except as provided under par. (d), no person under 12 years of age may obtain any approval authorizing hunting. (d) Restrictions on validity of certificate of accomplishment. A person under 12 years of age may obtain a certificate of accomplishment if he or she complies with the requirements of s. 29.591 (4) but that certificate is not valid for the hunting of small game until that person becomes 12 years of age. (2) Persons 12 to 14 years of age. 29.304(2)(a) (a) Restrictions on hunting. No person 12 years of age or older but under 14 years of age may hunt unless he or she is accompanied by his or her parent or guardian, or by a person at least 18 years of age who is designated by the parent or guardian. (b) Restrictions on possession or control of a firearm. No person 12 years of age or older but under 14 years of age may have in his or her possession or control any firearm unless he or she: 1. Is accompanied by his or her parent or guardian or by a person at least 18 years of age who is designated by the parent or guardian; or 2. Is enrolled in the course of instruction under the hunter education program and is carrying the firearm in a case and unloaded to or from that class or is handling or operating the firearm during that class under the supervision of an instructor. (3) Persons 14 to 16 years of age. 29.304(3)(a) (a) Restrictions on hunting. No person 14 years of age or older but under 16 years of age may hunt unless he or she: 1. Is accompanied by his or her parent or guardian or by a person at least 18 years of age who is designated by the parent or guardian; or 2. Is issued a certificate of accomplishment that states that he or she successfully completed the course of instruction under the hunter education program or has a similar certificate, license, or other evidence satisfactory to the department indicating that he or she has successfully completed in another state, country, or province a hunter education course recognized by the department. (b) Restrictions on possession or control of a firearm. No person 14 years of age or older but under 16 years of age may have in his or her possession or control any firearm unless he or she: 1. Is accompanied by his or her parent or guardian or by a person at least 18 years of age who is designated by the parent or guardian; 2. Is enrolled in the course of instruction under the hunter education program and is carrying the firearm in a case and unloaded to or from that class or is handling or operating the firearm during that class under the supervision of an instructor; or 3. Is issued a certificate of accomplishment that states that he or she successfully completed the course of instruction under the hunter education program or has a similar certificate, license, or other evidence satisfactory to the department indicating that he or she has successfully completed in another state, country, or province a hunter education course recognized by the department. (4) Parental obligation. No parent or guardian of a child under 16 years of age may authorize or knowingly permit the child to violate this section. (4m) Hunting mentorship program. The prohibition specified in sub. (1) (a) and the restrictions specified in subs. (1) (b) to (d), (2), and (3) do not apply to a person who is hunting with a mentor and who complies with the requirements specified under s. 29.592. (5) Exception. (a) Notwithstanding subs. (1) to (3), a person 12 years of age or older may possess or control a firearm and may hunt with a firearm, bow and arrow, or crossbow on land under the ownership of the person or the person’s family if no license is required and if the firing of firearms is permitted on that land. (b)
1. In this paragraph, ” target practice” includes trap shooting or a similar sport shooting activity regardless of whether the activity involves shooting at a fixed or a moving target. 2. The restrictions on the possession and control of a firearm under sub. (1) do not apply to a person using a firearm in target practice if he or she is accompanied by his or her parent or guardian or by a person at least 18 years of age who is designated by the parent or guardian.