Hello!
Ah, firstly, bless you NN for saying such kind things about me - that's made my evening :)
I'm no qualified specialist in PND - my experience is purely first hand as a mum. I think what you're trying to do is really good, the intention is fab, but I will just pass on some feedback from a focus group I set up on how to get the best from a group.
We made a decision that the group would be a self help community resource for mums to talk informally among ourselves about life experience but NOT to advise on anything medical. We have sought support from our Children's Centre and my HV also attends to offer signposting for mums who might benefit form extra help. We are very careful not to put ourselves in a position of authority given the vulnerable nature of mums and our lack of qualifications.
We did consider having a mental health professional present and we may still have one as a visiting speaker but we agreed the group wasn't intended as medical intervention but as a support resource for isolated mums who simply could go somewhere on a regular basis to meet like-minded mums.
As for childcare - we encourage mums (and dads) to bring babies/toddlers with them as we think the interaction between parents and children is a fundamental part of PND - and the early years co-ordinator who has helped me to devise a potential programme of guest speakers, is qualified to provide activities for the little ones.
There are lots of groups out there - with lots of different formats - each with their own merits. Just be careful you're not making yourself (and others) vulnerable by trying to be advisory rather than simply being yourself (a mum with valuable first hand experience of the horrors of PND).
Hope that helps. Take care and good luck.
ps. my job really isn't that high powered - I've clearly bigged myself up!!