There is a very large parking lot on this side of the border. It's a pay lot but the prices are reasonable. Make sure you have cash. Also make sure you have some change for the turnstile when you walk across. We used to walk across for lunch about 3-4 times a month. Can't give you exact prices because we haven't lived in Weslaco for about 3 years now.
Considering the temperatures in South Texas, leaving any living thing in your vehicle for 4 hours isn't a good idea. If it get's warm and the cops are called, they won't hesitate to break a window to get the pet out. You might want to see if someone in the RV park will babysit you're baby for a couple of hours. Although we don't have any of our own, we used to babysit furry babies once in a while for that very reason. Plus, the parking lot is a dirt field surrounded by farmland so the security can't be guaranteed; although I've never heard of anyone losing anything there.
Don't know that much about the 1015 park except that it's obviously named after the famed Texas 1015 sweet onions. You should pick up a sack, you'll be there just about the time the 1015 fair and harvest happens.
