It's quite common for kids to fall sick when they start childcare and they are more expose to germs there.
You can give some supplements daily to boost their immune. I used to give my kids sambucol (http://www.iherb.com/Sambucol-Black-Elderberry-For-Kids-Syrup-Berry-Flavor-7-8-fl-oz-230-ml/57291). It is very good especially if your child gets runny nose.
The other supplement I gave was childlife first defense (http://www.iherb.com/ChildLife-First-Defense-4-fl-oz-118-5-ml/6367).
Also feed them lots of fruits and vegetables. If your child is prone to fever, maybe you can consider boiling some barley once every fortnight.
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