oh debbie, i think it is such as shame that you had a bad experience with your mother's group/playgroup. i have been meeting with my first born's mother's group for over two years now. and i have to say they are a fabulous bunch of women. however, we do treat mother's group as a mother's group. it is for us to talk openly about any concerns or problems or successes we want to share with each other. we have been meeting at each other's houses which means it is a safe environment and allowed the children free play for the morning that we meet. from my experience mother's group has been so rewarding for not only my son, but also for me. i have formed friendships that i know will last a lifetime and my son has made buddies that he too will have for the rest of his life.
however, i do understand your desire for something more structured for your boy. my son gets his structured play from other activities such as gymbaroo and mini maestros. i don't know if this is an option for you, but these sessions are great, because they are playing and learning at the same time. each week we learn a new song to sing at home or a new activity to practice at home.
i hope you find what you are looking for...