Does your son drink a lot of minerals before going to bed at night? i think alot of kids have this problem and most of it turns out to be lazyness not wanting to get out of the bed at night time, why don't you start a routine of waking your child 2-3 times at night to get him up to go to the bathroom weather he has to go or not, see how that goes for you i know it will be very exhausting but at least it might solve your problem.
It is not laziness - it could be a medical condition - he needs to see a doctor! There are many reasons why a child that age would still be doing this.
I think this post is a joke. Who keeps their kid in diapers until age 4????