This might be a dumb question but. Do you have to reserve or pay to use the tables at the picnic/bbq area? Or is that just to ensure you have that space for your party?

The tables and shelter area are free, but they are first come first served. Each vehicle must pay for parking and there is no nearby alternate space to avoid the fee.

for my daughter's bday, i got there at 8 to get my tables. party started at 2

There is street parking available near the N. Santa Fe entrance. There are picnic tables, restrooms, and a playground at this entrance.

Yes, there is a day use fee, per vehicle ($3), when you drive in. If there's a particular table you wish to use, then come early to ensure you get it.