See your child's health care provider to discuss your options. There are medications that help. My son is on one called ditropan. It seems to be working quite well!
In the event that he does have an accident we have his mattress protected with a "Zippered Vinyl Mattress Protector" from Walmart paid $6.88. It encases the entire mattress! To eliminate the crinkling plastic sound, I put a waterproof fitted mattress cover/w quilted top on the mattress before placing the fitted sheet.
I have an ample supply of the quilted mattress covers and fitted bed sheets, so my son's bed can be remade immediately instead of having to wait all day for laundry to be done.
Here are some other tips:
We let our son load up on fluids early in the day. He stops drinking anything by 6p.m.
Remember that caffeine causes frequent urination, so give it sparingly. Our son gets caffeine only if we are on a family outing or hosting parties. He's only allowed to drink up to 12 ounces of a caffinated beverage, and only during the Lunchtime hour. If we're at a restaurant, he orders water to accompany his caffinated beverage, just in case he's still thirsty. (He's learned to flip his empty cup down to prevent the hostess from topping it off with more soda! LOL)
Before bedtime he is reminded to use the restroom.
He sets his alarm clock for 1a.m. so he can get up in the middle of the night to void. The alarm clock is placed clear across his room so he has to physically get out of bed to turn it off, otherwise he'll turn it off by his bedside and fall back asleep.
If he wants to sleep-in on the weekends, we still wake him around 7 or 8am to have him use the restroom, then let him crawl back into bed.
His medication has to be taken on time, otherwise he will experience nighttime enuresis (bedwetting).
I hope I was helpful. My son is also 12, btw.
P.s. I forgot to add one more tip!!!
If your children's mattresses have been soiled with urine. An easy way to remove it is with "OUT". It's a bacteria & enzyme solution that permanently removes new and old pet stains and odors! One day my son's urnine leaked down the side of his mattress (before I purchased the zipper cover), and I freaked out. I ran to Walmart to purchase carpet cleaning solution in an effort to save his new mattress. Right by the solution was the "OUT". I figured if it removes urine stains for pets then it's bound to do the same for humans! haha! It worked! The stain and odor was lifted in minutes after I soaked the section that was soiled! Just to be on the safe side, I added 8-ounces of "OUT" to my carpet cleaner and gave it another good scrub. WOW!
Oh yeah one other thing, to eliminate the lingering stench of urine in your children's pajamas and bedding, wash their soiled clothes in HOT water only.