My DS is 4.3 years and has been toilet trained since he was 2.2 years, over the last year he has only had 2 or 3 accidents in his bed (wees never poos). He has had a plasic sheet on his bed ever since potty training started, (he caught on really quick and was dry at night before being dry in the day) but now I don't know when to remove it. Any ideas?