I share your preference to limit the plastic toys, but I don't think an invitation requesting "no plastic toys" would be received well by the families of some of your children's friends. Over the years, my kids have had parties where they requested donations for a cause they cared about instead of gifts - pet food for a shelter works well because their friends can pick something out to bring to the party. We've also had some 'no gift' parties. Some people had an issue...