My dd is 2 yo and we use medium FB during the day (one snap left at leg, tightest snaps at waist) and then we use large FB at night. We end up overlapping the waist snaps to keep the large snug enough on her waist and keep the dipe from drooping - it doesn't look super-nice but it seems to work, keeps it on snug enough that she seems comfy and the dipe stays put. Haven't had too many problems with leaking, but I have begun putting in a hemp doubler in between two terry or other fabric inserts for nighttime, since the hemp holds a lot but doesn't catch it fast like the microterry does. I've found she does best with a microterry insert closest to her, then a hemp, then whatever other insert I have (I have some older inserts made for FB that I got used from a mom on eBay, I think she made them - the work great but I've no idea what's inside them) - usually it's a nice thick microterry insert that I bought from a WAHM on eBay.
For me the biggest problem I have is that the mediums are not enough for overnight but the larges gap at the leg - that's why I use some pretty thick stuffing for inside, so I can stuff it up and keep the gap at her leg from causing leaks. So far it's working pretty well.
HTH and good luck!
Heidi
For me the biggest problem I have is that the mediums are not enough for overnight but the larges gap at the leg - that's why I use some pretty thick stuffing for inside, so I can stuff it up and keep the gap at her leg from causing leaks. So far it's working pretty well.
HTH and good luck!

Heidi