Good advice from others. Yes you can get the chicken pox again if your immune system is down how ever if you have had them, the sx the second time around would presumably not be as severe. You said you have had the chicken pox already :)
I strongly agree you should talk with a medical professional first to see if you should continue exposure to the child with chickenpox.
That does not make you unreliable as a day care provider but wise in taking care of yourself. Bless you.