The 3 year old boy was moved to a pre-school so there is now only DD 26 months old, a baby girl 7 months old and a new baby boy 3 months old. DD still loves going and happily marches in there but I start to really feel that she does not get the stimulation that she needs.
She's 26mo, the stimulation is there, if she is happy, it doesn't have to be from older children etc, there is a huge issue within schools with the idea (from parents) that the only way children are extended is by more or next step work etc... the reality is that the best extension is actually in "mastery" & "teaching" which is where they skills they have are used to show others how to do it etc... ie a child who is really good at times tables working out a way to help a child who is struggling, will actually develop better skills long term than a child who's moved on to more advanced Mathematical concepts.
When we pulled Ds1 from daycare at 28mo (because I wasn't going back to my job) I did heaps & heaps of research on the social side... 4yo is the age that peers start to matter. DS1 went back & started preschool at 4.5yo (to the day) before that we'd done Library, swimming, & a sports group, but he really had no interest in other children... by 2 months in he loved playing with the children & he absolutely wasn't behind on his social skills etc - in fact long term he's done better than children who were in daycare from much younger ages (could be many reasons, but the fact he was in a big centre when he was "wanting it" (ie we increased the days because he wanted to go so much) made a huge difference/
At 32months old we tried DS2 in a daycare (I did contract work from home at night etc so I was at home with them) because DS1 was in preschool & DS2 had lost his play mate... it was HORRID, DS2 started biting his brother, he we his bed etc... it was too much he was happy with just the Library & swimming lesson then at 3y8mo when he started preschool he was better, but it really took until he was about just over 4yo before he started to make friends & be social before that he just sort of hung... this is the child who at 11yo has a busier social life in a month than an A list celebrity!
The Scandinavian model of daycare (family groups of 4-6 children of multi age with one carer in a centre) has shown that children actually do better in that environment than a whole group of 3yo who are all at the egocentric age.
I personally think you need to listen to your DD's happiness at where she is at & block out the big business daycare noise that says she's missing out & go with the fact she's happy with where she is & keep her there. At 2yo connections to an adult are about 100 times more important than playing with another 2yo (or rather playing sitting next to).