Potty Training

So Tyson has been doing great at potty training, except at nights.  None of our kids have ever had problems at night, so Steve and I are at a loss on what to do.  So the other day he had an accident during his nap, so I cleaned him up.  Then he turned and said "Mom thanks for taking Sarah and me swimming, it was fun."  I said, "We didn't go swimming I have been cleaning."  Tyson said,"No we went swimming and it was fun!"  I asked, "Do you go swimming a lot?"  He said, "Yes you  take Sarah and I all the time."  Now we all know I don't so now I have figured out his problem....apparently every time he goes swimming he wets the bed...so now to waking up in the middle of the night to keep him from peeing the bed and dreaming of swimming...