Not to worry too much (I know it's hard...), I was also so worried when I first went back to work. My son's now 3, but I am still worried..
But, I keep telling myself to have trust in the maid, afterall we all know the most concern is danger issue. If she's not doing her work well, as long as no danger, no problem. And I think we must treat the maids good ourselves, so that they are happy to take care of our children.