That woman thought because you were older than her son, you should give him your soccer ball and buy a new one for yourself. (I've seen your other posts from reading them I think you mentioned are a teenager or 20ish). You should say that sounds like a good reason and let her son keep the ball. Then go take her purse (with car keys and all) and say that you want it and because you are younger, she should just go out and get a new car and purse.
Afterall that was her reasoning.
Seriously, I can't believe anybody would let their child take something from a stranger, let alone expect that stranger to give it to them because they are a ccccccchhhhhhhhild. The fault would lay on that mother (or whoever she was) if he thinks it is OK to behave that way and gets hurt because of it.