For the younger bridesmaids you could make them up a sort of goody bag, not tacky, get a nice box and put in some hair pieces, and little girly bits, as they are slightly tricky to buy for! for the older bridesmaid, a nice necklace or bracelet she can wear on the day? Bit tricky to get them all the same thing when there is a big age gap between the youngest and eldest! Good luck!
Look at the Hurley Burley website. They have some lovely things. You could get them all matching necklaces. They do shorter sizes for the younger girls. Free delivery, everything I've ordered has always come the next day. Also 10% off at the moment. Lovely children's necklaces from only £10. I've placed a few orders with them, always been very happy. Just ordered myself a key ring yesterday.