What size did you make the mickey heads. I printed 5x7 and 8x10 for the adult shirts, DH thinks 5x7 is too small. Please share pics if you have, thanks.
I would measure an appropriate distance, both vertically and horizontally, on a shirt and see what you think looks good. Or print out some Mickey heads in draft mode on plain paper in various sizes. Place on shirt and see what works!!
When I do shirts for adults I use 8.5 x 11 sheets and fill the sheet as much as I can. For kids shirts I print two graphics per page. I have never had a problem or a complaint.