3 yo DS scared of other kids. how can I help him?

[movingwest]

Finding it really upsetting actually. He is 3.4 yo and at playgroup 3 mornings a week. He is a confident happy little boy at home but when around other children he is extremely shy. He has a speech delay of up to a year so I had blamed that for his shyness.

But recently he is petrified when another child bounces up to him or tries to play with him. There was an incident where a very boisterous 3yo went a bit mental and sat on him, he couldn't breathe and it really shook him up, and I am sure that has contributed. This kid is at his playgroup and is one of a few very rough little fellas who DS cowers from. We are moving away soon so he will be starting again at new groups/making new friends.

All I want to do is help him to socialise and be confident (especially given his speech delay) as it breaks my heart to see him like this .
Can anyone give me tips?

Could you invite one or two of the less boisterous children from play group back to your house for playdates?
If he gets to know them and make some friends in the safety of his own home, he might find it easier to be confident in the playgroup environment too.
My DD is quite shy and she finds new people, places and situations quite hard until she relaxes and gains confidence. Having one of two friends in her preschool really helped her to settle.