A 7 year old wetting the bed is pretty normal and usually nothing to worry about.
Bed Wetting is mostly caused by weak bladder muscles because the bladder muscles are not getting strong like they are supposed to as the child grows.
Then as the child gets older the muscles in the bladder get stronger and eventually the child stops wetting the bed.
Bed wetting usually goes away by 8 or 10 years old but sometimes can last into the child' teenage years.
You can take your child to the doctor who can prescribe your child some medication that helps decrease urine production overnight so that your child's bladder does not get too full.
You should also have the child go pee right before bed to empty their bladder which can sometimes help stop the bed wetting.
If the child will wear some bed wetting pull ups have them wear the pull ups or even some diapers overnight to help keep them dry and comfortable.
You can also try a bed wetting alarm as well as they can be pretty effective if the child is not a very sound sleeper.
Other than that time is usually just the best remedy for bed wetting and having them wear diapers if possible to keep their bed and them dry.
Having some tests done would be a good idea just to rule out any other things such as bladder infections but if it's just caused by normal things then the child will usually eventually outgrow the bed wetting in time.