The Fairfax school bus will pick up and drop off your child at the daycare, if it is within the school's boundaries.
Yes, they may provide a bus stop there. But it isn't guaranteed. And there has to be a minimum number of kids that ride to the stop. I go through this with my kid's after care every year. Every spring they tell us there won't be a stop. Then enough parents request a waiver (coordinated by the after care provider) and FCPS provides the stop again. PITA.
So it's easier if the after care provides their own transport, but often that is a higher fee.
It's actually somewhat easier if your kid goes to a home daycare. Then they just get off at the regular stop for that address. But again, you have to request a waiver for your kid to get off at a stop that is not their address. It's a TR-52 bus form "REQUEST FOR EXCEPTION TO RIDE A SCHOOL BUS".
http://www.fcps.edu/fts/tran/eligibility/exception.shtml