Got an invite to spend a couple days up there coming up. Is there much to do on the island? We will have our two kids (3&8) with us. Anywhere for them to swim? Will be staying at a privately owned house if that helps. Should I take a car over or not?

Nice island, haven't been there in a few years, but it was always my favorite island to spend with the kids. Not as commercially developed as South Bass, at least it wasn't the last time I was there. There's a nice beach at the state campground. Take bicycles if you can.

Thinking about just leaving the truck at the ferry Parking and just taking bicycles over.

Of you want to, rent a golf cart while over there.

I'm not 100% sure if the north beach is public or private. However the north side of Kelly's is about the most beautiful area to anchor a boat off of and float. There is a nice Beach there but I really don't know who owns it to swim from. There is also a yacht club up on the north side..

There is the glacier park on Kelly's  - it's something to do/see with kids too. Also some small shops in town to go around.  

You can also hop the jet express to put-in-bay to see the monument before its closed for several years.

Edit:

Their is a state park with a beach on the north side. I thought so but wasn't sure.

Timely topic.  We're headded up there Sunday for a few nights.  We were just going to leave the car at the ferry, but you have to pay for parking anyways.  Just got a nice big tent and it weighs a ton.  Since I'm the only pack animal in the family I get to carry all the stuff.  Executive decision to take the car!  $16 each way is worth it.

We'll be renting a golf cart too.  The boys love to drive it around.  Remember to bring saran wrap for a make shift windshield.  Bugs are a pain in the eye.

The island has a winery and brewery.  I'm set!

Put-In-Bay is on South Bass Island.  Middle Bass has / had Lonz Winery.

with the price of golf cart rentals there I would come out ahead to buy one and sell it at the end of the weekend