My 5 children are with Kim Dawson. It is really fun and good at helping them associate with adults. You can look at their website www.kimdawsonagency.com and look under models and then children. It has been my experience that if you would like representation, you should send two photos of your child...one a headshot and one full length (baby should be sitting up). The pictures should be ones that you took---not professional ones. And, you should keep sending them every 3-4 months...as your child grows and changes.
You can also try the Campbell Agency. Good Luck!