Here are a couple ideas:
You can indicate it on your reception card for an adult only reception
or
You can put a note in the wedding invitation stating:
"please let us know if you need to arrange childcare on the night of the
wedding and we will be happy to give you some references".
Hope this helps!!
Krista-
Wedding, Bridal & Baby Shower Table Cards, Place Cards, Favor Tags, Note Cards, and Programs