My son is now 25, but when he was 3 or so, I let him choose what square was next. He felt so proud, he was helping mommy, and for years I had a remembrance of our day together. He had this large space to fill up with colored squares
You know, he still has what I call an 'engineer' brain. Even when given a coloring book, he'd make a geometric design on the paper, like the picture wasn't even there, very engineer-like
He grew up to do something in computer networking, I'd explain it but that would mean I have to understand it!