While I am sure your organisation offers a very worthwhile service, it is a commercial and a national one (I've looked at the Baby Sensory website). As such (and this is only my personal view) your use of the website for free advertising, (even as a FoSAP 'member'), is a cynical misuse of the function of the website. I feel the FoSAP website should not be used for such advertising. Otherwise your initiative becomes the thin end of the wedge whereby the website becoming a useful organ for any business to sell its 'wares'.
The proper place for such advertisements is the local magazines 'Bishopston Matters' and 'Bishopston Voice', which I imagine you have already contacted. You do course have to pay for advertising in these publications.