Ask first, if you can pick them up at any time during the period of time that they are at the daycare.
That is a way of asking, if you can drop by at anytime without first calling. If they say no, then i would find out why, or seek out another daycare.
If they say yes, then consider that one, but in the mean time, ask to use the restroom. Take a look around while you are on the way, and even look in the rest room to see if it has been cleaned.
Ask if you can use the phone, then take a look around. You just never know what you may see.