My mom and I were debating this today because it seems like toddlers are a hard group.

Our center has young/old age groups. So:

Young Infants are 3-9 months (not mobile)
Older Infants are 10-14 months (mobile)
Toddlers (15-24 months)
Young 2's/Older 2's etc.

I guess my concern is that there is a big difference in a 15 month old and a 24 month old. The toddler room seems like it's the only one not split.