Just so you know, some doctors recommend being careful with melatonin for kids since it’s a hormone and there’s not a ton of research on long-term effects. They say it might disrupt sexual development during adolescence. Kids produce more melatonin naturally and it is though that a reduction in melatonin production during adolescence is actually what triggers pubertal development. Might be worth looking into a bit more before making it something regular.
When I brought up melatonin with a sleep doctor a few years ago she agreed with my understanding that given a lack of uncontroversial studies its unclear whether it is a health risk or not.