Thanks for all your replies. By the time I had finished typing my message, I had almost convinced myself that I was making a mountain out of a molehill, and I would find a lot of you saying 'come one Tigermoth, don't be such a wuss', only more politely of course. Thank goodness I pressed the post message button, otherwise my son's friend's parents may well have received a note next week from me - aka person unknown.
I think it does get harder the older they are. I am getting past the special-trip-to-the-playground stage with my son, so as a neutral meeting place it isn't such a winner - and it's difficult to arrange too long in advance at the moment because of the weather. An easier option in the summer.
My son has given me an idea of who his friends are, and I know the two most talked-about by face already. What I don't know is how well they play together, so I will ask the teacher about this aspect. We had a nighmare situation at my son's old school. It was only when my son invited a certain 'best friend' his birthday party, that I realised how badly they wound each other up and egged each other on - and realised in a flash why this friend's mother had refused two playdate invitations. She had the benefit of seeing them play together after school each day. Anyway, that was my first and last attempt to date at engineering a social life for my son via school.
Anyway, I like Mollipops suggestion of sending out notes to the parents asking them to phone me about a possible meeting for the boys and us. As you say, by putting the ball in their court, they are not put on the spot.
Cfr and Janh, as you say, I think it's also a very good idea to invite the mother to stay for the first time, it will help stop any fears on her behalf. If I do this, I'll keep the playdate short. I'd find it bit daunting having to entertain a strange adult as well as a strange child. And when the school has a social event, I'll definitely get the teacher to point me in the direction of the appropriate parents - thanks Janh.
Sml -as for taking my son to school more often, I am trying to do this - actually, I am trying to adjust my working hours permanently to make this possible - but then I'll be getting back home even later in the evening, sigh!
Robinw - that's a very valid point you make about not finding my son's friend's parents on the PTA.
(Ps Robin, my son did not get a computer, but he may soon get internet access - as I hopefully will - via my old laptop. And the new school has lots of computers as well. Dh is fighting the prospect of having a computer in the house, but knows it's a losing battle)
Callie and ChanelNo5, I like the party idea, too - my son's birthday is in the spring so I might wait till then. I will definitely invite his school friends to any bash we hold. Possibly as Callie says, I will invite all the boys in his class, if I am feeling brave enough and get lots of help. As Helen says, I can go the parent route first and organsise a small parent's social bash. I may do this when I feel I know peopel a little better.
Also, do you find you make unfortunate snap judgements about the parents you see when collecting your children. I often find myself thinking so-and-so looks nice, not like that hard-faced one over there. I may start chatting to the nice friendly parent only to see them later hugging their teeny tiny year 1 child who has nothing in common with my 7 year old, while the unfriendly-looking one is the mother of my sons favourite classmate.
Anyway thanks again for replying. Any more comments, keep them coming.