Child designed shirt, how to?

[MC0810]

My 6 year old wants to design his own shirt. Most likely a drawing of mickey. I dont want an iron on, but rather have his drawing printed on the shirt.

What is the best way to do this?

Should I have him draw it on paper and scan it into the computer, or ir there an app he can draw with on an android tablet? I also have photoshop to make any necessary edits.

what website should I use to order the shirt?

Thanks, our trip is in 3 weeks