OP,
I'm the pp who originally suggested Kingstowne and the areas outside of Belvoir (near Beulah gate),... Island Creek Elem area. I just did a mapquest for you coming from that part of Kingstowne/Island Creek and I did it again coming from the Van Dorn side of Kingstowne (further East). It was 25 from the east side and 30 from the Island Creek area to Census. that is at 3:00 p.m. on a Sat. You can assume it would be worse (maybe 10 min. or more, I don't know) during weekdays rush. FWIW, the heavier traffic is moving from Md. in the morning into Va. So, you would be going somewhat against the grain. But, the Wilson bridge (b/t Va. and Md. can be traffic clogged).
I also mapquested from central Bowie (Whitehall school district -- which is the highest rated one or one of the few)... to Census. It was even further than coming from Kingstowne!
You will not be able to live at Andrews as a civilian and you wouldn't want to.
I'm glad you liked the Kingstowne area. I figured you would!! Your child will totally fit right in. No one will bat an eye at a biracial kid. It is so easy to get around -- the roads were planned/built more recently and they are wider and just easier/less stressful than some of the older parts of Alex./Fairfax. The commute from Island Creek area (western part of Ktowne area) is 16 min.
With you being the primary parent, I think keeping commute consistently at 30 min. or less is key so that you can pick up the child on time. There are always rentals in Kingstowne proper (which is its own HOA as well as a general area and town center with movie theater, shopping, restaurants). The HOA has a pool and various activities. Same with Landsdowne HOA. Island Creek also has a pool, but not as many community events... but some.
If you are looking for child care, I would go first with Northern Va. Academy Landsdowne. Second choice would be La Petite Academy or Little Acorn Patch.
Good luck!
These are a variety of rentals:
http://www.zillow.com/homes/for_rent/Franconia-VA/house,condo,apartment_duplex,mobile,townhouse_type/5XhvKT_bldg/31636_rid/2-_beds/38.76465,-77.142488,38.75615,-77.160491_rect/15_zm/
http://www.zillow.com/homes/for_rent/Franconia-VA/house,condo,apartment_duplex,mobile,townhouse_type/2096544894_zpid/31636_rid/2-_beds/38.765243,-77.136169,38.748243,-77.172175_rect/14_zm/
http://www.zillow.com/homes/for_rent/Franconia-VA/house,condo,apartment_duplex,mobile,townhouse_type/51971311_zpid/31636_rid/2-_beds/38.753397,-77.149966,38.736394,-77.185972_rect/14_zm/
Even though the last one doesn't look as nice, it is in a great community, closest to Ft. Belvoir, Wegmans (you will love), and Nor. Va. Academy.