If it doesn't hinder you in any way from taking care of their children, then it doesn't matter. In most places, disclosure of your condition is required by law, while in others it is not. I would mention your condition, but only in passing and in a manner that puts the issue aside. Such as, if they say you can eat their food, you can say thank you, but I often prepare my own meals to watch my sugar levels. If they press, be up front with them. The worst thing you could do is not tell them and the kids mention you testing yourself in front of them or have them see your kit. Be honest.