In this case, Ben suddenly remembered that he wanted a seven on his tee shirt because he used to have a "four" tee that was passed on from his friend John. And he knew that John's mom had sewed it, so mom, make me a seven tee shirt already!
Holding the baby, I directed him to make a newspaper template for the numeral. Then he pinned it to the fabric of his choice (his favorite green) and some non-fusible interfacing. I zig-zagged the fabric to the interfacing (no need to get out the iron for fusible interfacing, see) and then shortened and widened the zig-zag and sewed the seven onto his shirt. Ben chose orange thread - doesn't that look sharp?
Done. And happy!