Yeah, that's what I mean, if they were human then they were probably only in infant or young children's sized clothing at the time of mutation.
Kind of odd to have size appropriate clothing thrown around though. Maybe they just use it to disguise themselves to go grocery shopping or whatnot. Now, the sweater (on the chair) makes good sense since it might get kinda chilly down there.
Crazy alternate theory... the clothing belongs to their victims.