Can definitely recommend both the tour and museum, unless its changed you're with a tour guide the whole time and its fascinating, the one running the one I went on was really enthusiastic and really interesting to listen to you could feel his passion for United. You get to sit in the dug outs and have photos etc. You can get a little guidebook as well which will be interesting for you to read afterwards as it has lots of extra detail in.
I recently recommended the tour and museum to a friend who was booking it as part of her husband's xmas present and they took their children, you don't mention how old your son is I think from what they posted on Facebook after the kids didn't really pay much attention during the museum but her husband loved it but they had younger kids so yours may be older and more interested, he may be anyway so its worth going, not having children myself I'm not sure what way round I'd do it eg tour then museum or museum then tour. I think they have an exhibition dedicated to our treble winning season on at the moment which I bet is really interesting to see.
One thing to note is they don't do the tours on match days (I think the whole day but correct me if I'm wrong)
I also don't seem to remember the tour including features such as the statues and it must have done but I'm not entirely sure it featured the Munich clock but it surely would? So its definitely worth walking round the ground before hand and showing him these things/ getting some photos etc he will probably enjoy listening to you telling him about them