Hi! Another mom asked a similar ? of her 6yo son the other day - following is my answer to her, but keep in mind children are so, so different & you can't compare a boy's progress to girls at all. 4 1/2 isn't that old in the grand scheme of things. I have twin boys so every day is a science experiment & the wetting at night issue was a huge difference.
It takes some kids' bodies longer than others to figure out the whole "don't wet yourself in your sleep" thing. This was extremely frustrating to me, having twin boys - one who decided just after he was 3 that he was going to wear underpants 24/7 & did it no problem, & the other just seemed to get into such a deep sleep that it didn't matter even how many times I woke him at night - he was still wet at least once a night (sometimes more) & in the morning. There definitely seemed to be a bladder-release-upon-waking thing. I restricted fluids after a certain time, woke him numerous times each night, read all the nice stories that are out there about staying dry, etc., but I think in the end it was just a matter of his body maturing in the right way. From what I've read in the various bedwetting books & online, a child's body begins to create less urine at night (rather than "holding it"), but for many kids (particularly boys, but some girls too) this process doesn't happen as quickly. Reading books, talking/explaining, begging, scolding - none of that worked - eventually, while he still did wet, the amount began to lessen to the point where I didn't have to change the whole bed, all the clothes, practically bathe him completely, etc., and only put down a thick beach towel under him.
Note to all of you saying EWW, gross, unsanitary, etc.: really not all that unsanitary - everything got washed every day, he got washed every day, but we just really needed our sleep - it was taking quite a toll being up all night doing laundry & trying to ensure him staying dry (which never really did happen until his body was finally ready - just over 7 1/2 years old).
Good luck to you - it can be stressful but hopefully your son will get there sooner than 7 1/2! My husband just kept reminding me that he won't graduate high school & still be a bedwetter. Smile -