Re: Hajj
Umer, I went on this year's Hajj and must say it was quite tough at times. I can only imagine how tougher it would be with a child. There was one young couple with us on our tour group who had a child with them and were constantly having to shuffle him between the two of them to get some 'free time'. Also bear in mind at Muzdalifah the toliet facilities are very very limited and waiting in the que can be 30mins+ on average so avoid it. The chances are you will have to clean him on the ground. Besides its only one night there and keep plenty of disposable plastic bags with you to dispose of diapers, sterile wipes (remember to pack plenty), rubbish etc. If indeed you will have more family accompanying you as you say, then it will be much easier. Considering the sheer volume of people it is very easy to get disorientated and lost from your group so stay very close together.
Most importantly if your wife chooses to go to Jamarat you will have to arrange someone to take care of your son as taking minors into the jamarat area is an absolute no-no, especially on the final day when the stampedes occured. Adults can barely manage to hold onto each other. And once that is complete the coach journey back to Mecca takes 7-8hrs. Its total gridlock as all pilgrims are all heading back in the same direction. By foot it would take 1-2hrs which is fine. Its best your son sleeps through this phase as it can be very frustrating. Find out from your tour group where specifically the Dubai camps in Mina are. ie. how far from Jamarat. The Western Europe/N. American camp sections are over 30mins walk away.
Also tour groups paint a very rosy picture of their services but once you're on the ground with 2million other people, things are very different. Nearly everyone picks up some sort of throat infection so make sure your group has given you all details about medical assistance. A sick child will only complicate matters further so consider mouth masks (cost 1 riyal each) for your family. A lot of pilgrims use them to protect against infection and the pollution out there. I used one and it was pretty helpful. Buy and pack your own antibiotics beforehand rather than waiting.
And lastly make sure you work out plenty. Your physical strength and endurance will be put its extremes.