My friend and I took my 8 month old twins on a summer weekday. The zoo was very busy with other families and day campers. Even so, parking wasn't too far from the entrance, the line for tickets went very quickly, and we were able to get around the area freely without traffic jams.
It was quite sunny that day that we were there, but there are so many trees, overhangs, and indoor attractions that we were able to stay cool and no one got sunburned.
There is one indoor area that does not allow strollers, so be ready to carry any little ones.
If you have more than one child, I suggest using a tandem (one seat in front of the other) stroller or a wagon for easiest maneuverability. The wide jogging strollers are more difficult to get around the indoor areas. There is a wagon rental just after you enter the zoo - don't know the pricing.
Food is available in several areas of the zoo and some healthy options are offered. Otherwise, coolers are allowed, so pack your own food, snacks, and drinks to save money.