How do I help with very shy/anxious toddler

[Talou1]

Hi my ds is 3.5 years and is very outgoing and lively when in an environment he feels comfortable in but he is very shy and anxious everywhere else. He suddenly became clingy about a year ago (when he changed nurseries)and is now very shy. Won't speak when spoken to, clings to me at parties and playgroups, won't have one to one conversations with the carers at nursery. Today we went to a party that was underway when we got there and he had a massive tantrum and refused to go in. I had to take him home. He had a baby sister 4 months ago and alternates from saying she's his best friend to wanting her to go back to the hospital. (I know this is normal) But how do I help him? He has another 3 party invites but I dread taking him because he will cause a scene. One friend said I pander to him when I help him out when people talk to him but what else do I do, let him flounder? Do I take him to the parties knowing he is anxious about them. (He does usually settle down after about 20 minutes - but not today) Or do we avoid parties, but where will he learn to overcome his shyness if he doesn't socialise? Now when his grandparents want to take him out he won't go if it means I am alone with his sister. I know he is insecure because of his sister's arrival but I don't know how best to tackle things when he is naturally a bit insecure anyway. Also, since his sister's arrival he has massive tantrums if he does not get his own way. Please tell me this will pass! Any help/advice would be appreciated.

ds1 is not yet 3, but also extremely shy, to th point that his tantrums in public have been silent, or that he won't cry if he falls and bumps his head in public. he's always been like this, and we've asked for lots of advice. the consensus is that we shouldn't push him to do things he doesn't want, encourage people to talk to him without asking questions as that avoids him feeling under pressure to answer (this is actually really hard to do!).

he is getting better, and now has friends he talks to at nursery, and last weekend went to one of their birthday parties quite happily (although he wouldn't talk when there).

also, you could try small playdates (eg just one friend) in his home, in the hope being in his own environment feels more safe. then build up to going to the friend's house.

can't help with the new sister part, so far we've been lucky with ds1 on that front.

Thanks MamaChris. Good idea re people talking to him without asking questions. I know he feels under pressure when he feels he is expected to answer. Good idea re small play dates too. Thanks for your help.