C.R.
We belong to a playgroup and have for years. I also put my boys in sports at a local church. Though I agree that friends are important, picking good ones are even more important. You don't need a huge group of kids for your children to learn good social skills, especially when they are under the age of 8. I think children should be able to stumble and make mistakes in a safe place with support and guidance within their own family. As they age their world will expand and the skills learned today will come into play. I was a teacher at a private school before becoming a mom. I can tell you that a group of young children can easily become a "gang" mentality pushing some children out and making others feel superior. Alot of peer pressure. I think that young children need to understand and feel good about themselves before being exposed alot of children. Providing a strong foundation for the decisions of tomorrow.
I have found that most home schooled children are quite able to socialize with all ages/gender/race and not only their own peers. It's because they are in the day to day life not put away in a classroom with only children their age. They are learning not only academic skills but every day life skills with you.
And of course who is going to care about their education more than you? They will be blessed to have you as their teacher :) as you to have them as your 'students".
As for entertaining them, I don't think that it's necessary. They can learn to be self sufficient and learn to play on their own. Just my two cents. Wish you well with your decision.
C.