According to the DSM-5, in children a gender dysphoria diagnosis means meeting six of the following eight criteria and experiencing "significant distress or impairment in function" as a result that lasts at least six months:

• A strong desire to be of the other gender or an insistence that one is the other gender
• A strong preference for wearing clothes typical of the opposite gender
• A strong preference for cross-gender roles in make-believe play or fantasy play
• A strong preference for the toys, games or activities stereotypically used or engaged in by the other gender
• A strong preference for playmates of the other gender
• A strong rejection of toys, games and activities typical of one’s assigned gender
• A strong dislike of one’s sexual anatomy
• A strong desire for the physical sex characteristics that match one’s experienced gender

Again, as in adults and adolescents, a clinical diagnosis of "gender dysphoria" does not require a child to have negative feelings about his/her sexual anatomy or physical characteristics. At all.

A child must simply prefer clothing, toys, games, items, friends, roles etc that the child has been taught are typical or stereotypical of the opposite sex - and/or to desire to be the opposite sex, or to have the characteristics the child associates with opposite sex, for whatever reason.

https://www.psychiatry.org/patients-families/gender-dysphoria/what-is-gender-dysphoria