FWIW as a secondary teacher, I think we are aware that all the students who have been out of school since March (new Y8/9/10) will need to be "transitioned" back into school and that all students will need extra support throughout the autumn term (and some will need it beyond that).
We're also aware that some students missed quite a lot of work during lockdown, whilst others have done a lot, and some will need quite a lot of support academically. As a school, we have made plans around review/catch up- I'm sure most schools will be doing this.
I do unfortunately think some friendship stuff could be tricky- for example, at my school, the Library won't be available to students during break and lunch, and at the moment we don't think we will be allowed to run clubs, either. Having to spend all their time in a year group bubble could be difficult for some students socially too. Obviously we will do what we can to support students pastorally, but there will definitely be aspects of this that will be tough for some students with the restrictions in place in September (which are obviously necessary).
Nothing about this situation is ideal, schools will try their best, and I think if you have real concerns then it may be worth talking to school a week or two in. However, equally I would try to be calm/reassuring/encouraging at home- things may not be as bad as you/they fear.