Look at the child find services for your area so you can get a list of both in-home and daycare services locally. Make sure you are part of the listserve for your kids school. Sometimes people post on there to find someone to do afternoon pickup. Look into which places can provide daytime babysitter services. You need flexible but you also don't want to be scrambling at the last minute to find where to look and verifying the quality of those options. I know people that have had good luck with Monday morning moms
http://www.mondaymorningmomsmcmd.com/ for in- home if you are in Montgomery County.