Just wanted to recommend this....we took DS yesterday (2.10 years) and he loved it! Under 3's are free so great value too. It was a brilliant day out especially given the rain yesterday and we more or less stayed for the whole day (it's open from 10am to 5pm) having to strike a deal with DS about the gift shop in order to get him to leave! There are fab informative exhibitions aswell as mini set-up areas ie garage and cafe where the children can let their imaginations run wild as it's all very interactive.
The cafe isn't up to much and can be quite expensive so we took a picnic, which we were able to eat in the seating areas and as we could come and go from the museum, it meant we didn't have to lug the cool bag around with us.