First, rule out the OT Saranac. It is OT's bottom of the line boat and nowhere near the quality of their other canoes. Those molded seats may look cool, but they are one of the one of the tricks mfrs. of cheapie canoes use (along with keels and aluminum supports) to support the chintzy hull. They also make kneeling impossible if you feel a need to lower your center of gravity. 16 ft is the absolute shortest length you should be looking at for a family of four.
Jason mentions that his canoe feels "...more tipsy with kids moving around, but it felt easier to paddle. I also feel like it was harder to tip although it more "tipsy".... That feeling is known as primary and secondary stability. Primary stability is how "tippy" the boat feels when getting in and out and moving about. Secondary stability is how hard it is to actually tip over. In most cases canoes with good secondary stability have low primary stability, and vice-versa.
With the kids in the boat you probably are looking for one with good secondary stability.
Consider buying a used higher end canoe, instead of new cheap, rotomolded or thermoformed garbage like the OT Saranac, Pelicans, Rogue Rivers, Colemans, Sun Dolphin, etc.
Some to consider:
Wenonah Spirit II
Mad River Explorer 16
Old Town Discovery (169 or better yet if you can find it, 174)
Mad River Journey 167
Bell (now Northstar) Northwind 17 or 18
As far as material, it's hard to beat Royalex for the combination of durability, weight and cost. Unfortunately the company that makes Royalex discontinued its manufacture, so you won't find many "new" Royalex canoes unless they are older leftover stock. If you can find a Royalex boat used and in good condition, jump on it. A lot of canoers are hanging onto their Royalex boats now because they can't purchase new ones. Kevlar is light weight, but more fragile than Royalex. For use on a lake it's great, but don't use a Kevlar boat where there will be a lot of rocks. Many canoe mfrs. have moved to multi layered Polyethelene to replace Royalex, but it's heavier than Royalex versions of the same boat.
Aluminum will last practically forever (unless you bend it around a rock in a river or a tree falls on it), but they generally have crappy paddling characteristics. However a 17 or 18 ft aluminum canoe may be a inexpensive option for you now and in a few years you can give it to the kids to use as a beater boat, while you and the wife upgrade to a better canoe. Or you can sell it for about as much as you paid for it.