Even with some of the areas closed for renovation, this is one of the best museums and gardens I've visited, especially with adults and children.
The natural history and world history and culture areas were fascinating. Not too big that it takes ages, but enough detail to suit all levels. Lots of hands on activities for children, especially the musical instruments area.
It's free to enter, but you pay to go into some areas. Knowing we would return, we just paid this time for the aquarium, which was great - informative and well laid out, though didn't actually take long to go around.
The gardens are fabulous, not too far to walk around and interspersed with areas of interest for kids, like the musical garden and the animal walk (llamas, rabbits etc).
The cafe is good with seating inside and out. Not a huge choice but reasonable prices for this type of place. Be aware the kids' pizza is big - easily enough for an adult.
There's no parking, but we drove around the housing estate and found a place easily.
We will definitely return, especially when the renovated areas are open.