Causes of bedwetting
Bedwetting is usually a combination of factors and is rarely caused by a physical anomaly. It can happen that a child produces more urine at night than other children. Stress can also play an important role.
Bedwetting never happens because your child drank too much during the evening. And your child also doesn't wet the bed because it sleeps too deeply. However, your child doesn't wake up as easily.
The cause of bedwetting is often that the child has not learned (yet) to become aware of a full bladder during the night. A full bladder transmits a signal to the brain. The brain must then learn that this signal means a need to wake up. During the day, children are much more aware of this process. That is why children are usually sooner potty-trained during the day than at night.
Luckily, it means that there is no physical issue. There's only an issue with timing! And the timing of going to the bathroom can be taught through training.