I only have one but no I don't think they run small. In fact, DS fits a teensy bit better into the 12 mos Children's Place blanket sleeper than he does his Carter's one of the same size. (The difference is small, like maybe the Carter's shrunk more in the wash or something).
I love ours! It's a shame there was only 1 in her size!!! It fits great, and is honestly my favorite out of ALL sleepers I have! I do have a tall and skinny baby though... =/ So I may not be much help.
Re: Children's Place Blanket Sleepers
This has been my experience too. SUPER super skinny and long..they don't work well with our cloth diapers!