You can hear the roar of the waterfalls as you walk along the level, well-marked trail. There are plenty of streams to throw rocks into and fuzzy caterpillars to stop and look at. When you get to the end of the trail, you walk across a bridge at the base of the waterfalls and feel the wind and spray of the water. Your kids will be in heaven.
We went in Spring, so the waterfall was at its fullest. At that time, there is no way you can let your kids get close to the pools at the base of the waterfall or anywhere near the slippery rocks.
Although this trail can get overcrowded, we did it early in the morning on Memorial Day weekend, and found it pretty quiet.

This is a pretty big visitor center, but most families won't spend more than 20 minute here. Though, you'll need more time if you hit the bookstores. There are a few cool exhibits, but nothing very kid-friendly.
You'll want to hit this visitor center if you need information on the park.

This science museum is smaller than most others in the Bay Area, but it does have enough exhibits to keep most school-aged kids engaged for at least an hour or two. The traveling exhibits are always great, but our two favorite permanent exhibits were the outdoor lab area and the animal discovery room in a classroom downstairs. I wished we would have had time to check out the planetarium show.
The views from the outdoor play area are awesome. So sit back and relax while your kids try their hand at controlling the water flow "from the Sierra Nevada".
Check the schedule for the times for the Animal Discovery Room, since it's not always open.

If you're in Chinatown, it's worth making a stop at the Fortune Cookie Company. You step into a tiny store, get to see the women making the cookies at the machines, and get a sample. They have some bagged cookies to buy for about $5. It can get crowded if there are more than a few tourists at a time, so you may not get to hang out in there for longer than five minutes.

I wasn't really a baseball fan until I had my son. We try to catch a game at the park at least a couple of times a season. I love the views from the top decks. It's pretty relaxing. The kid area is great for those tots who can't sit through all the innings. Even walking behind the bleacher section, and ringing the bell on the cable car parked out there is fun.
Oh, and who doesn't love a park that serves Ghiradelli ice cream sundaes?
Sign up as a fan through the Giants website and you may get some emails with coupons. We even got a good deal for club level seats last summer.