Nancy, make sure that the set screws on the hook are really secure. I'm wondering if they were a tad loose.
It's actually pretty easy to mess with the timing if he was rotating the hook by hand and playing with the handwheel. Especially if the hook screws weren't tightened fully. I think the 319, FW and 301's have similar hook screw configurations and can go out of time much easier than on other machines.
Nancy, just remember that the tip of the hook needs to be dead center on the needle above the eye. You'll do it, just like before;>.
I guess I'm more of the mind that a 4 year old is expected to get into things. That's just the way it is. We, as the grown ups are the ones to expect that and to act accordingly. If that means putting items up or away to avoid temptation, so be it. My kids used to get into all sorts of mischief and that's what learning and growing is all about. A curious mind is a growing mind.
You've not been around much, Nancy. We've missed you!