If your contract says 3 kids, I think they have a right to refuse. And I don't agree with the others that you are entitled to change these terms, unless it is clearly stated in your contract that you can do so.

I personnally suggest that you take that off your contract for next time (at renewal) and explain to the parents that you are entitled in Ontario to have 3, and now feel that you could easily manage. Give them some confidence, they just seem anxious! You could also tell them that you financially need the extra money (without going in deeper explanation as this is not their business).

If they are too stubborn, tell them right away that you will fulfill your end of the contract but will change this clause at renewal, if you renew with them now knowing how they don't have confidence in you and they don't respect you as a person either!

Sarah