Sleep troubles

Hi brave mommies!! My Dec 16 born 4 yr old boy is still having trouble sleeping at night. Anyone else having or have gone through the same problem please share. I have a 4 month old boy also and its getting very difficult to manage both at night. The 4 yr old does not take any nap all day and wakes up late and gets up several times often at night. Any medication which would work for him. Due to Covid its very difficult for us to take him outside and make him do any physical exercises and he has only virtual school.