After living in the area for over 2 years this is only the second visit to Rancho La Aurora and I'm not sure why.  We will definately do it more often from now on.  The kids just refer to the place as 'los toboganes'.  We arrived about 11am and were only the second group there - by 4pm there were about 15 groups but not at all crowded.  Admission is about $40 pesos for adults and $25 pesos for kids.   You can either bring your own food and drink - or they have a restaurant and small store.  Lots of room and lots of shade - we parked in back next to our tables.  The water pumps for the slides are not always on and that may depend on the amout of people there to pay the electric bill.   Still - very fun place!