I haven't run into this but, sometimes with the coins if there aren't enough in the hopper it starves (kinda like a boat cavitating) it runs out momentarily and the optics don't see enough coins passing and it throws an hopper empty code. You will never get (at least really unlikely) a hopper to pay out every coin before it times out. I've hit pays too big for the amount of coins in the hopper and had to add coins to get it to finish. Basically the same thing. Add more coins and it should fix your problems. Also, any time a kid plays, they will hit bigger payouts than you or I ever do. Kind of goes along with how slot machines reproduce. It's an unstoppable force. Glad they are having fun with it.
Dave