Since then we have been fanatical about never using them as a source of credit. We got the cards through our bank, and about once a week we go and transfer money from our checking account to our CC to pay off whatever we used.

For us at least, it seems to have been working.
We’ve never gone in debt with them, and have never let the credit card tempt us. With self controll, I think they can be a good way to build a good credit rating.