Hi there - there used to be quite a thread going in "Other subjects" but a lot of people don't post any more.
The agencies that seem to be around a lot at the moment are Kids London, Bruce & Brown, MOT and Urban Angels. Other well known names are Norrie Carr, Elisabeth Smith, Bubblegum, Scallywags. There are plenty of other reputable agencies so don't panic if I haven't mentioned one you've heard from! Who have you applied to?
My DD is with Bruce and Brown - she's 4 now, we were with Norrie Carr from age 1 to 3. They got her quite a bit of work at around 1 - 2 years old (one of her old pics is in this month's - September - issue of Mother & Baby, she's the blonde girl eating a slice of melon in the toddler section and on the contents page) but I felt that Bruce & Brown were better when she got older. Also, Norrie Carr charge £150 or so per year for pictures/website/promotion and you have to buy copies of the pictures they take. Bruce & Brown just charge £35 for website admin, which they deduct from the child's earnings, and £110 for the pics but you get a CD of all the pics they take. I think it might be less for babies - the over 3s go in their "model book" which is circulated to clients - they don't do that for babies as they change so much.
The upside of modelling is that you can get some lovely stuff to look back on - we have magazine pictures, a Boden catalogue, hopefully the next Woollies catalogue and pics on the M&S website in the autumn. All money is paid direct to your child either by cheque or to their account.
The downside is that everything is v short notice - you could get a call at 4pm asking if you can go to a casting the next day. Also, a casting is no guarantee of a job, so you could travel into London, spend 10 minutes at a casting, then not get the job. Sometimes you may even get the job and find the pictures are never used - my DD's first job was for Next - I was so looking forward to getting the catalogue, but they didn't use her pictures in the end. She got paid for it still, but it would have been so nice to see her in the book.
Good luck!