I don't think any of the above answers your question - probably because it can't be answered without quite a bit more info. - as helen indicated.
However, as a generalisation if your husband was already working above 30 hours p wk & you (as a couple) were already getting both child & working tax credits then any increase in income (i.e. total income for the two of you) would result in a reduction in tax credits. But this would not come about straight away - it would probably not happen until the next tax year after you started work.
So if the above is the situation I can't understand how your child TC went up, & NO - it should not go up again if your hours increase.