I'm actually reviewing the JetBoil Sol (aluminum version) right now and will start work on the Sumo this coming weekend if you can hold off a week or so.
If you do get the JetBoil, I'd get the pot size appropriate for the type of trip you'll most often take. For example, if you do 70% solo and 30% with your son, I'd get either the Zip, Flash, or Sol. If those percentages are reversed, then I'd get the Sumo. On the type of trip you take the most, I'd use the JetBoil pot, but on the type of trip you take less frequently, I'd just take any old pot or pan and use the adapter that comes with the JetBoil.
JetBoil pots and pans are quite expensive, but with the adapter, you can use any pot, pan, or kettle you like. Here, I'm cooking an omelet on a JetBoil Sol burner -- but I'm using an MSR Blacklite pan.
So, like I say, buy the efficient but expensive Jetboil specific pot for the type of trip you take the most and use a regular pot or pan for other trips.
Note however, that the JetBoil is not my favorite cooking stove. If you fiddle with it though, you can get some nice results. Here's an omelet I prepared on a JetBoil. It turned out great.
More to follow when I'm done with my review.