Albert Barnes on Matthew 12:27

By whom do your children, etc. Christ was not satisfied by showing them the intrinsic absurdity of their argument. He showed them that it might as well be applied to them as to him. Your disciples, taught by you, and encouraged by you, pretend to cast out devils. If your argument be true that a man who casts out devils must be in league with the devil, then your disciples have made a covenant with him also. You must therefore either give up this argument, or admit that the working of miracles is proof of the assistance of God.

The words of Christ, here, do not prove that they had actually the power of casting out devils, but only that they claimed it, and practised magic or jugglery. See Acts 19:13.

Your children. Your disciples, or followers. Mt 1:1.

They shall be your judges. They shall condemn you and your argument. They are conclusive witnesses against the force of your reasoning.

(y) "Beelzebub" Mt 13:24