What is the current entrance fee? And is there an additional pet fee? Also, does this need to be paid in cash, or do they accept cards?

Four dollars, no pet fee. Cash only

Maryland residents are $3 weekdays and $5 weekends. Out of state visitors are $5 and $7. This is per person, not per vehicle unfortunately, but it's a bargain to help keep places like this open and well managed when you really think about it. Also, cash payment has always been the only option so far as I'm aware.

Is this per person? And are children in safety seats still free?

$4 for Maryland residents. I think it's $6 for out state.