We went when Scoot was three. It was great but he kept wanting to shoot off ahead and you can't go back IYSWIM (once you go out of the big doors to the outside, you can't go back in the main hall again) I think you might want to be able to keep her in one place on occasions, if you actually want to have a proper look. Anyway, the buggy is always handy to dump bags and coats in and abandon randomly

that's what we end to do anyway. Not sure about things to do in watford; we went to a swimming pool somewhere and then had a picnic in the park before heading to out time slot. Have fun! Oh and the shop is rather pricey! Scoot was desperate for a wand but they only had the proper replica £25 ones.