Yes. If you are registered as self employed and are paying tax then yes you have every right to put in a claim for Working Tax Credits (although this is means tested). You should also be eligible to claim for the Childcare element of WTC, if you use registered childcare.

Edited to add: you should be getting Child Tax Credit anyway ( as this is the title of your thread) unless you're in receipt of a very high income.

You have to be working at least 16hrs a week if you have a child and at least 30hrs a week if you don't.

So if someone can only do outcalls and only gets 1-2 one hour bookings a week it can be difficult to claim as you would need to be spending quite a bit of time dealing with the business side ie taking calls, answering emails, updating ads to be eligible.