Wokerman, the definition of "Public Funds" in paragraph 6 of the Immigration Rules has not yet been changed.
That is, it still includes "Working Families' Tax Credit", which was abolished on 31.03.03 .. and does not yet include Child Tax Credit or Working Tax Credit that came in as from 01.04.03.
Accordingly a claim to Child Tax Credit cannot possibly breach any condition on a visa.
Do however note that Child Benefit is within the definition of Public Funds, so hopefully you have not claimed that.
The relevant part of the Immigration Rules can be read here