One of our free outings recently was to the Children's Gardens at the Huntington Library in San Marino, California. First Thursday's of the month are free entry to the entire library.
What a great experience! I was prepared for anything since it was free, but since it is normally $15 per ticket I expected something great. I wasn't disappointed. I took my 2 1/2 year old and my 10 month baby. I was surprised at the sheer size of the facility. Be ready for a hike akin to Disneyland or the ballpark. First you hike to the front gates and then to the Children's Gardens. So take a stroller. Although it won't be allowed into the gardens, there is plenty of stroller parking just outside.
Their website does a great job of describing the different elements in the Children's Gardens and I suggest you read it before attending. However, I was surprised at what a fantastic job it does catering to toddlers - even my 10 month old.
It was a hot day so we spent the majority of our time at the Water Bells - a water feature that includes several fountains that drain into a river that is large enough for the children to wade in. The part that I loved was that the fountains were low enough to the ground that my now-standing-baby was able to play by himself at the fountains. He LOVED it! No one had to hold him or help him. He was just like the big kids.
I felt it was much better than the outdoor sections of the Kidspace Museum. The Kidspace Museume focused more on school-age kids and my daughter spent most of her time bored, reaching or scared by the large statues of insects. Perhaps more toddler friendly activities will be added, but for now Huntington Library Gardens is my favorite.
I would highly suggest sunscreen and a backpack for water and snacks. Lots of kids were wearing swimsuits and water shoes. Some kids were even sitting in the river fully clothed. It was a crowded day since it was free, but if you can afford it I would try to go in the morning midweek - just to beat the crowds.