Just want to add my two cents here.
The SS is open to all ages. But that said, the first time we took it, it was ruined by several cranky, screaming toddlers. They were making so much noise that we couldn't hear the guide.

The one right behind me was flailing around and whacked me in the back of the head a couple times.
It was obvious that the parents hadn't fed the kids first (DUH!) and that this was a time of day that these kids were normally very active, so sitting still in a tram wasn't working for them.
Of course some babies and toddlers would have no problem with this type of experience.

But not all, and parents need to think very carefully about how their children will react to this tour.
I was very upset about the first SS experience--spending $100 to be whacked in the head and miss about 80% of what the guide was saying due to some out of control children who's parents didn't have the consideration to think about if their kids would enjoy it or not. (These kids did NOT enjoy the tour, and made it rather impossible for other guests to enjoy it either

)
The second time we went on it, there were also some younger kids. They were well behaved, although towards the end the toddlers were getting restless. I would have given them about another five minutes before they would have begun to get disruptive. Kids are kids, and most babies, toddlers, and pre-school/early elementary aged kids have attention spans that are only just so long. Parents need to be aware of their kids and what they are and aren't able to handle, and act accordingly.
If you do decide to go, feed your kids first! And if your kids are very active first thing in the morning, you might want to get them up even earlier to let them run off some steam. Also, the second time we went, the people with younger kids sat in the back of the tram. They had the same view as everyone else, but when their kids started to get a little restless it was much less intrusive to the other guests.
Even if you decide that your kids aren't up for the SS yet, I'd still suggest the AKL. It's a wonderful, magical place, and the concierge staff there is simply the best Disney has to offer!
Anne