The pain will slowly, gradually, decrease IF the child is allowed to grieve and express feelings. Daily life contains many hidden pitfalls for children who have lost a close relative. New friends ask how many siblings are in the family. Other kids complain about their parents. A girl's first period without a mother around.
Children deal with bits and pieces of reality as they mature.
Grief may seem to resurface years later. The child might withdraw, mope around, act out, be on edge, or cry. Be sensitive to what may have triggered it. Talk about it, if they want. Express your love.