8 year olds wet themselves at night because they have a bladder that is not growing as fast as it normally should and the muscles of the bladder are not developing properly and so they release the urine at night into their pants instead of being able to hold it.
They also don't produce the proper hormones to wake them up when they feel their bladder is full.
It is normal for an 8 year old to wet themselves at night.
Bed wetting in children is very common and normal and nothing to worry about.
Some kids will wet the bed until age 17 or 18 years of age and some kids may stop wetting the bed by 5 to 10 years old.
It depends on how fast the kids bladder grows and develops and some kids bladders grow more slowly than others.
Myself I wet the bed until I was 17 and it sucked but I was healthy and nothing else was wrong with me.
Finally after age 8 my mom suggested to me to wear diapers and at first I didn't want too but finally decided to try it and it made a big difference as I was kept dry and the bed and sheets and my clothing were dry and I was more comfortable.
They also make pull ups for older kids such as Goodnites but tape on diapers are much better and more absorbent.
I have a 7 year old son that also wets the bed and we tried Goodnites with him but he is such a heavy wetter at night that they would leak and get the bed wet.
So I started buying him some Gentle Steps size 7 diapers from Dollar General which are very absorbent and are mostly plain white.
He prefers to wear those Dollar General Gentle Steps size 7 diapers and they don't leak on him and keep him dry.
He also wears them on long road trips when he may fall asleep or can't hold it until we get to a toilet.
Bed wetting is nothing to be ashamed of and many kids wet the bed and nothing can stop it other than medications which I don't trust.
Bed wetting is different than daytime potty training and some kids just need time to outgrow the condition.
If your kid is potty trained and continues wetting their pants after age 5 then it may be a health issue and the child may have a bladder infection, urinary incontinence etc that should be checked out by a doctor but bed wetting or nighttime wetting in kids is normal.