What to do in Altrincham or Manchester with 3.5 yo and baby?

[PortAndLemon]

I will have DS (3.5) and DD (2.5 months) all to myself at a loose end for four hours or so on Friday afternoon. We're staying in Altrincham but near the station so I assume that Manchester would also be a possibility, and will have the car so somewhere you need to drive to would work too.

Any suggestions for something that will occupy a very active three-year-old for the afternoon?

Museum of Science and Industry in Manchester. Free (well except for Bodyworks special exhibition, which I wouldn't have thought you would want to go to with a 3 year old). It's near G-Mex Metrolink Station.

Oooh thanks, that sounds great!