DS is 2.5. He has never been to nursery but stayed home with me or GPs/uncle and due to strict lockdown where we live (abroad) he has had no in-person interaction with other kids for months and months, and very little with adults except close relatives and the doctor, shop assistants etc (masked). Parks were closed so he barely saw other kids let alone played with any. Now things have started to open up we have begun going out on walks to busy places, to the cafe, park, playground, shop etc but he is terrified. He cries, wants to leave/go home etc. If other people speak to us he avoids eye contact, looks away and physically hides if possible, wants to go to the far end of the park away from other children. Afterwards he will ask questions/talk positively about people(especially kids) he saw, he just can't cope in the moment. I try to reassure him without pushing but I'm so worried that the lack of socialisation due to covid has been really damaging for his social development.
I'm sure part of it is personality - he has always been very clingy with me and a bit wary of other people (adults/kids), liked to observe for a bit first but once he got used to the situation was fine and got stuck in. With people he knows he is boisterous and very chatty. This summer is especially tough as it involves a lot of changes, we are moving to a new city and currently staying with relatives, it has been a bit stressful for him and he seems to be back in a separation anxiety phase.
He is due to start nursery/preschool in September, with a big class of over 20 kids (he'll be among the youngest). I know 4 months is a long time but it's so hard for me to imagine how it won't be traumatic/awful for him. I really want to use these 4 months to help him adapt to all the changes in his life and prepare socially/emotionally for the experience (aside from the practical stuff like needing to potty train him) but I'm not sure how to achieve that other than very gradual aclimatisation. Does anyone have any advice/books or videos to recommend /a similar experience that turned out well?!