Logan is the youngest of the 'light' sides.

This headcannon is actually backed up with science, because when a child is born the first thing they develop (sorry if spelt wrong) is anxiety then comes creativity then morlity (again sorry if spelt wrong) last is logic. and the reason I said 'light' sides is because later on in thomas' development decit and introvie (listen I'm not good at spelling and I'm tired) thoughts depending on factors of course.