I use several and have had a good experience with them all for my boutique Pinky Winks Boutique if you want to look at some of my modeled photos on my Facebook page that I have been getting back.
Here are the ones I have been using:
Simply Posh Models
Little Diamond Models
Little Angles Boutique Models
I have a 20 month old boy listed with Simply Posh and Little Angels that would love to have some bookings: http://www.facebook.com/photo.php?fb...type=3&theater http://www.facebook.com/photo.php?fb...type=3&theater
So far, it looks like booking for boys are not as common because fewer boutiques have items for boys.