My 4 1/2 year old has started to pee in cups and hide it, the this morning I found a bag full of wee hidden in the cupboard. He says he doesn't know why he is doing it. What can I do and how should I react? He is toilet trained and is not doing this at night, its being done during the day. He does not have a fear of the toilet because about 98% of the time he uses it with out a problem. Please help.