Welcome to Healthcare Magic forum.
Crying in the night in toddlers usually occurs due to some discomfort or pain commonly abdominal pain
due to gaseous bloating, ear pain
due to cold or infection, or leg pains due to growing up pains.Another cause can be unpleasant dreams or nightmares
In your child it is possible that he had pain in legs.Growth pains occur due to the rapid growth and stretching occuring I'm bones of children and is a normal phenomena.some children are especially sensitive to pain and are troubled by it whereas others do not feel it .There is no specefic treatment needed and it usually subsides on its own.Sometimes calcium supplements
are prescribed by doctors if a deficiency is suspected, to promote adequate bone growth.
So as of now its nothing worrisome but if is persistent and disrupts his sleep then do consult a pediatrician
Wishing him good health.