While ScottC presented this as a way to dress your kid up as a baby Cthulhu, unfortunately they only come in pink and blue. Surely there would be a way to dye the thing a dark, brackish green, yes? If so, then you would truly have a Great Young One on your hands.
Then you hand the kid a baby bottle that says SOULS on the outside. See? Instant costume to disturb your in-laws with.
I would like to go ahead and say this now: if you have a kid and you dress him (or her!) as something twisted, I want pictures. Send them and I'll post them as part of our usual Halloween mayhem.