Rebecca, my daughter (age 4) was recently seen by a pediatric urologist (for another issue) and we had a lengthy conversation about this very subject and I will tell you what he said.
Acheiving bladder control at night is a complex issue. The bedwetting child literally sleeps through his or her bladder signals. This is especially true of deep sleepers. They have absolutely no awareness of bladder sensations during the night, let alone how to control it. Also, there are hormonal factors in play as well, and for some children the hormonal control of ADH (anti-diuretic hormone) may act differently. Simply put, bedwetting is a communication problem between brain and bladder.
Withholding fluids or cutting a child off at a certain time will do more harm than good. Children need a great deal of fluid in order for their bodies to function properly. Restricting fluids can cause dehydration and constipation and at the end of the day, it does not "teach" your child anything about waking up in the middle of the night to go potty. They simply stay dry because they don't have enough fluid to actually need to urinate. Therefore, you've done nothing to "teach" the brain how to detect bladder signals simply because there are no signals at all to detect. Restricting fluids is only done really as a convenience for the parents. The same goes for waking them before you go to bed. Again, you don't "teach" their brains to wake on their own since you are waking them up! There are drugs you can give them, but again, the drugs don't cure bedwetting, they just mask the problem by slowing down bladder function at night until your child can outgrow bed-wetting.
The pediatric urologist told us that the biggest "issues" kids seem to have with bedwetting are when they are away from home at sleepovers, grandma's house, etc. It becomes more of an embarressment the older they get.
He then went on to tell us that these issues usually resolve themself by the age of... are you ready for this... TEN!!! I was shocked when he told me that!
He did also tell us that, at the age of 4 (which is where our daughter is), doctors aren't concerned at all about bedwetting. But at the age of 6 or 7, they start to get slightly concerned about it. Your pediatrician will probably ask you to start keeping a diary. What is different about your child's day on the nights he/she stays wet or dry? Is there a relationship to food, drinks, events, bowel patterns, etc.?
My advice (take it for whatever it is worth), keep the diary from now until your child's 7 year checkup so you come in with plenty of information for the doctor to look at when you go in for your appointment.
I hope this helps and best wishes to you.