Swim jackets

I would like to get Sophie and Molly swim jackets for when we go away in September. I have been looking at floaties jackets on E-bay but they seem to come i the size 1-2, 2-4 and 3-6yrs?
Molly is small for her age and Sophie is teeeny. No Idea how big they come up or what ages to get? Worried if I get Sophie a 2-4 one it will drown her as she is 27lb and wears 12-18m clothes.

Anyone have any Idea what the sizings like?

Ben had a splashabout one which was 1-3 years. He wore it from about 8m until just a few weeks ago when he moved to armbands. So the sizing of that was spot on really - he couldn't have worn it for much longer as it was getting a little small.

I just sold it on eBay otherwise you cod have had it.