青少年是多少歲?

11歲以下係兒童
11-18歲係青少年

I believe 青少年means teenager, thus, the range should be 13-19. All of the numbers pronounce with "teen" at the end.

For 兒童, the range is not nery clear, but it should be under 13.

兒童１－１０歲
青少年１１－１８歲

兒童1-10歲
青少年11-17歲