I came home from work today to find that my 10 year old son had made a bow by himself after school. He found a green branch, shaved off any extraneous smaller branches with his pocket knife, and notched the ends. Then he grabbed the only bowstring substitute he could find, which was some old twine that I had in the garage. He said his other option was clothesline but he knew that would be too thick to nock the arrow. He tied the knots himself (he didn't do a proper bowline knot, but I feel like he can be forgiven). All I did when I got home was helped him tighten the string a bit by wrapping the ends around a couple more times.
He already has a wooden arrow that I bought him during a failed attempt to make an atlatl. This bow worked much better and he was able to shoot it probably 40 ft. I was very impressed with him. He just decided he wanted to make a bow so he took the initiative, found what parts he could and got it done on his own. He's growing into an awesome young man, but definitely too quickly.