The Visvesvaraya Industrial and Technological Museum on Kasturba Road is Bangalore's main science museum, and one of the better ones in India for hands-on exhibits. The galleries cover electronics, biotechnology, aeronautics, space exploration, and the history of Indian engineering, with plenty of working models and interactive displays. The two full-sized steam engines in the courtyard are a good introduction — they look industrial and important, and children tend to be fascinated.
The museum is particularly strong for families and for anyone with an interest in India's industrial history. It is not large, and you can see the whole thing comfortably in two hours. It sits on Kasturba Road just outside the eastern edge of Cubbon Park, and is easy to combine with the Government Museum and the Venkatappa Gallery into a full morning.