Why are you choosing not to respond?
If you are not seeing the children and don't want to then the courts are likely to make an order allowing for the current situation to continue.
If, however, the kids are with you and you're not letting the other parent see the kids - well, the court could make orders and if you don't comply with them, then the court can take action including fines and jail. The other parent could also make a costs claim against you.
Look - if you are not letting the other parent see their kids and not responding to the court application is simply continuing on with your attempts to prevent the other parent from seeing the kids, I reckon you might want to think this through.
You might want to provide a few more details so that the good folk here can give you more precise opinions.