Any recommendations for first time seniors thinking of buying a 3 seater canoe to enjoy with 2 grandsons (3 and 6) mostly on calm park lakes?
Rent first. Just the two of you.
Find a rental livery that has “plastic” canoes and try one out on a nice afternoon. Land it a few times and lift it, trying to imagine having to get it on or off the car roof or as far as you need to get a canoe to the water from where you’re likely to store one.
I’d be uncomfortable with someone else’s 3 year-old in my canoe unless everyone else in the boat was a competent swimmer.
Do you anticipate doing much paddling without the grandsons?
The weight of a canoe doesn't have a big effect on the water, but it does make a big difference in the ease of loading/unloading/tranport. If you cringe at the thought of loading it you won't use it. Lighter canoes tend to cost more, but a cheap boat you don't use is no bargain. I suspect that anything much over 60 pounds will be uncomfortably heavy for you.
There are hoist systems for your garage to make loading & unloading at home easier.
Youngsters may be more comfortable sitting on a pad in the bottom of a canoe than on a seat. Many manufacturers offer a third seat as an option. Snap-in seats are availible. There are also specialty child seats, like this one:
On many canoes it's fairly easy to modify or move the existing seats and thwarts. Lowering the seats will make the canoe feel more stable.
Don't overlook used canoes -- there's not much that can go wrong.
If your primary concern is stability on flat water, you probably want to look at "recreational"(aren't they all?) or "sporting" models as opposed to "cruising" or "tripping".
Wenonah Fisherman, Heron, Kingfisher
Old Town Camper
and many others. There are lots of boats that would work for casual use.
There's no substitute for trying boats on the water.
If you've never been canoeing, consider taking a lesson. Many novices get frustrated because they can't make a canoe go straight. In the summer I often see canoes in which both partners keep changing sides and arguing about who's to blame for the zigzag course.
We have a Bell Morningstar that works well for our "kids".
Great boat, but I wouldn't mind having a bit more room when it's 2 people + 2 75-pound dogs. The Royalex version of the Northwind is a foot longer and would be just about perfect for us as a "family" boat.
Some canoes feel "tippy" at first, but feel more solid the more you lean. Others feel more stable at first but get less predictable when you lean. Hull lenght, width, shape, and load are all factors.
Fisherman and others I know of…
The Wenonah Fisherman might look attractive because of it’s light weight, but IMO, it’s too small for two average adults and two children unless you can get those two kids to sit very still on the floor of the canoe and stop growing beyond about age three. I have one, which I really like - but it’s not a “family hauler”.
You could do it for sure with the Kingfisher, but it’s a bit heavy unless you get it in composite. The Camper would work until the kids grow some (had one of those too), but it takes a little skill to make it go straight on lake water. The Wenonah Heron might be okay if you are not large adults and the kids are small.
I wouldn’t be a bit afraid to put a couple small kids with me and the wife in my 16’ Prospector, but you’ll need to put some time into learning to control such a boat. Stability certainly wouldn’t be an issue though - once you get used to the “tender” feel.
Just to give an idea…
There are lots of boats that would serve you well. Here’s on that you should consider.
As long as you stick to flat water, that one should do all you want. For seniors, I’d not settle for less than Kev/spec or the Blue Steel construction. It looks expensive but would be worth it if you have the money.
I happened to check myself, and noticed that the royalex Wenonah Kingfisher is actually only 65lbs - which is lighter than I was thinking (over 50 memory). That’s not too heavy if you have a good wide rack system (it’s a 40" wide boat) and learn the easy way to load it. The trade-off will be that the hull is thin and flexes a lot, which will detract from performance. But that may not be an issue for you.
The Wenonah Spirit II might also be a good boat for you, with more performance.
Wenonah Spirit II
We have a Spirit II and it would do what you ask and more. A very stable design and a joy to paddle.