This will just take a few minutes. Collect some green sticks. Dead ones will break if you bend them.
The sticks must be very springy.
Cut a notch on each end of the stick. If you have broken the sticks, you probably already have some notches to work with.
Tie a knot in one end of your string. We had yarn, but it broke a few times. I recommend strong household string.
Work the string into the notched end, wrap it a few times, and knot it again.
Now bend the bow firmly and affix the string to the other end, wrap, and knot.
This bow had a little stub from a branch to tie the string to.
Find some arrows. They must have a little notch to hold the string and
they must be long enough to go from the hand which is holding the string, to rest on the hand which is holding the bow, and a bit further.
Now tell the children your safety rules.
The six and seven year old quickly got the hang of it. The four year old will learn with a little practice.
The baby had fun just holding his own bow.