Hello. You can take a look at here: https://goo.gl/dSgedh
There is a list of day care centers, maybe you can find something appropriate for you.

I am starting a new job in Falls Church this January and have a 6 month and 4 year old. We will need child care 2 -3 times per week, but the actually days of the week will vary (my husband's work schedule varies each month). Does anyone know of any centers or home day cares in the area that offer flexible or drop-in options? Thanks in advance!