DS goes to reception. I got a text today from one of the mums inviting him to around theirs to play and have tea. DS was excited but assumed me or his dad would go with him. He's never been alone to a friends house, and to be fair, he's only been without us on a small number of occasions (no family around, and not many friends with children his age). He absolutely fine at school but just does not feel that confident outside formal settings. Ideally I'd like to go with him the first time, but I do not want to impose, as she probably just wants to get on with her things.
Play dates are very short at that age, by the time they're home from school and had a little play it'll be tea time (5ish) and then you'd arrive. I'd just arrive early to collect and have a cuppa and chat then he'll be without you hardly at all. If he's really anxious have the first play date at yours maybe?