A birthday party or the park can present both a large number of children and many social situations concurrently. The demand for a high number of interactions and thinking on one's feet might feel like jumping into the deep end of the pool when one is not ready.
Might he be more comfortable with a play date, just visiting with one friend, possibly with a parent nearby as a coach if needed? Inviting another family on a trip to the zoo, museum, etc may also present an opportunity to practice friendship skills in a natural, comfortable social setting.
