My kids have both been in family daycare, 2 days a week from about 7 months.
DD recently started kindy, at just on 3, and she seems to be at just the right age to really benefit from the larger group of kids.
The reason we put her in was because at her FDC, she had been with the same three kids (one of whom was her little brother) for a long time, and she was the oldest out of the group by quite a bit.
As she got closer to three we really started to notice that she was "role playing" by herself alot and imaginary friends started to appear, and she just really seemed to be looking for that interaction with kids her own age that she wasn't getting at FDC. She loved her carer and we were loathe to pull her out but she has absolutely thrived in kindy and she literally cannot wait to go every day. The larger group dynamic has been really good for her communication and social skills, and she just loves it.
I think we put her in at just the right time.
Every kid is different but 3 was the magic age for her.