Hi and Welcome to Writewords
I spotted your other post about finding a publisher, so congratulations!
My immediate reply, here, is to seek representaton from
any agent; cast your net wide. If you are lucky enough to hook the interest of a couple of agents (even with a book deal it's not a given), then maybe come back and ask the question, but at the end of the day, having an agent is part business partnership, part marriage - you have to feel comfortable with them on a personal level regardless of whether they are one man bands or part of a large agency.
All the best
- NaomiM
<Added>PS, there are a limited number of agents specialising in childrens fiction - far fewer than those dealing in general fiction - and a lot of the one man bands are highly respected, so the size of the agency shouldn't be your first consideration.