Children really have no control over whether they wet the bed while they are sleeping or not. It's not something that can be trained into them. I wet my bed until I was 13, my daughter did until last year at age 9 and my 6 year old son is soaked most nights. He really wants to stop wearing diapers at night and I really want him to as well, but when we go with out it ends up with a soaked bed. Unfortunately, his body is just not ready. 3 years old is still very young and I know diapers are expensive, but I would go back to them for the time being.