This will be straight forward. I've sued for unpaid fees and won and I've talked a few carers through it too and they all won as well.
As long as your contracts are good, the judge will initially question you both to determine you really are an independent contractor/self-employed. Things like who determines hours, who determines location of work, who determines tasks etc. This is merely because employment laws are different.

Once the Judge is satisfied you really do fall into the realms of self-employed, then they'll look at your contracts. First glance, is it legal, signed by both parties, does it explain clearly or is it ambiguous. As long as it's clear, then the contract conditions will be upheld.

In terms of their counter claim - blah. We are in a position of trust and get to see things others don't. As long as the call to report them wasn't malicious, then you did what you (or any other concerned adult) is meant to. If every parent could sue those who express concern to CAS, then the whole system would fall apart.

Since it's your ex clients counter-claim, they will have to be able to prove it was malicious. It doesn't matter if your concerns were later proven unfounded (not saying that was the outcome). What matters is CAS isn't called just to stir up trouble for a family and if they are claiming you did that, then they have to be able to convince the judge of that.

Just stick to the facts, don't elaborate with your feelings, the Judge is not Dr Phil and he/she won't care about your feelings. Don't make statements you can't back up with documents or witnesses, don't get personal. Facts only with no elaboration/waffle/filler words.