Thanks for posts, all.
It isn't only me then!
mimsum - your DD sounds like my DS, in that it seems to be the act of separating, rather than the separation itself, which causes distress. This happens whether it's me leaving DS at school, my mum's, or with his dad even. Although I don't know about school, my mum and DS's dad assure me he's fine pretty quickly after I've gone, which is comforting.
Peachy - that's a lovely way to look at things: nicer to miss them than to feel glad to see the back of them! I do want to see the back of DS sometimes but not every day. I have a friend with three boys who is well-known to hate the holidays (I don't understand why she recently had her third, TBH), who told me how glad she was to see the back of half-term - even though a relative took the two eldest out on four of the week days! I know we're all different. I suppose I just don't understand that.
melissa75 and nickschick - thanks for your advice. I have been advised of similar things before, but I'm afraid I don't believe in some of these approaches. I realise that children mirror our emotions - so if we're anxious, they may be, too. So of course we need to keep an eye on our own feelings. But they do have feelings of their own! And, for me, in the context of a distressed child, going to the other end of the spectrum where it's all fine-and-dandy, nothing-to-worry-about, brisk-peck-on-the-cheek-and-depart isn't satisfactory either - it doesn't give the child any space to express legitimate fears (about separating from a parent, for example) and to feel heard. Also, there's an assumption that any anxiety the child is experiencing is automatically a mirror of their parents' feelings. A child separating from a parent at this age will often quite legitimately feel very unsure, in his own right, and I feel ill-at-ease with the jolly parent brushing over this.
All this said, I'm really not sure how to strike the balance between the two. Parents are generally not welcome lingering in a classroom to settle their child, and it's true that the parent has to leave eventually, so if it's going to cause distress when they do, they might as well leave sooner. So for all my ranting I don't have the answer!
I love the idea of the lipstick kiss on the hand, nickschick. I wear lipstick, so that could work a treat.
Thanks again for posts.