Puffling - 2-3 years is a notoriously difficult age - they are out of the "baby" range, and not quite in the pre-schooler range. You notice this if you look at catalogues etc (If I get one in the post I look at the kids modelling before the clothes/toys they are selling nowadays!)
DD2 had loads of work between 11 mths (when she started) and 2.5, then nothing until nearly 4, since then she has had 3 or 4 jobs a year (she's nearly 6)
Mummyegg - think it was you asking about UAN - I know that Mamas and Papas do a lot in Manchester, could be good for your youngest, as DD3 did a Mamas & Papas job at 4 mths, and they said it was a shame we didn't live North of London as they were shooting in Manchester the following week, and they do a lot there. (Think it's quite close to their Head Office)
DD3 has just done M&S baby girls, DD2 had a casting yesterday for Tesco back-to-school - more of an interview than a casting, they just asked her questions, chatted to her, didn't take any pics. She also has a New Look casting Monday after school.