I've worked with kids for years. At summer camps I run, they frequently call me "Uncle Mike".
Years ago one of the ways that we kept up with camp staff was through AIM (instant messaging) and a screen name was required. "Uncle Mike" made sense, however it was taken and rather than go "UncleMike789000078700" or some ridiculous number add on, I went with my initials = Uncle + MJM. Since then, that became my email of choice and formum SN as well.