I visited the museum on a Thursday morning and it wasn't too busy. My son is 9 months old so we spent most of our time on the 3 rd floor, it's geared towards crawlers and new walkers.
They had plenty of soft balls, large puzzles, and blocks for the little ones. They also had some soft padded mats that the babes are able to climb and crawl on.
Since it is a baby area almost everything gets put in the mouth. I'm not a huge worry wart but if you are then you will probably cringe frequently. The museum does have a tiny basket that is labeled "toys that have been in the mouth" but really we would've put half of the toys in the basket. Didn't really seem logical.
I may consider getting an annual pass once my son is older. For now $11 is worth getting out of the heat for a couple hours.
Also, I would pack snacks, their cafe is okay if you are desperate. Parking is limited so get there early. I would also recommend checking their website to see how many field trips will be there on a particular day. Sometimes there's 100's of kids scheduled to be there. Yikes!