I do worry about this quite a lot. My DS is two next week, and at the moment doesn't really see many other children on a regular basis.
We take hom to a p+t group once a week, and most of the children are around his age, but he doesn't really interact with them all that much. I've become friends with one or two of the mothers there, but we haven't met up very often outside of the group, partly due to my own shyness, I must admit.
It's complicated by the fact that my DP has depression and gets very anxious going out, but is my carer as I have epilepsy, and so neither of us are comfortable with me taking DS out by myself for very long. (I do still have fits fairly regularly unfortunately.) I'm also currently pg with DC2 due July. (Eek, I know!)
I worry that my DS isn't interacting enough with other children, but physically can't take him out all the time due to money and health constraints (the more tired I am the more fits I have). When children come here he is very friendly and shares his toys (almost a bit too insistently) but will often point at them and say 'baby' as though they are something to be observed rather than playmates.
I know when he turns three we will be able to take advantage of state-funded pre-school, but until then we can't afford childcare, as I'm on ESA with my partner home too as my carer. We are exceedingly skint, to the point where going swimming regularly or taking him to many activities is beyond our budget. Parks are great in the summer, but the weather has really exaccerbated this in the last few weeks.
My DS seems very happy, and is polite and friendly to everyone, as well as content in a group situation, so I'm not worried about him being nervous - only that I'm being horribly neglectful.