Professional references like from your dentist or doctor or lawyer who can say they have known you (and your family) for x years and have enjoyed a good professional relationship and they could say how much they like having you as a client/patient.
Also, having your police check, cpr and making sure you have a safe well thought out daycare environment also shows that you are a person who is taking this business seriously and has an eye for detail and place safety as a top priority. All these put together add to a positive and trusting impression for a potential client.