Rejection of design for kids/babies

I just got a design rejected for kids/babies.
The design is for a t-shirt that says “When I grow up I want to be an alien” and has an alien face on it.
What possible reason could their be for rejecting this for kids/babies.
Please explain so I can argue against this as it is clearly ridiculous.
Thanks

@Slum_City

Please contact legal@spreadshirt.net to get detailed informations.