Preparing for Beach Vacation

We live by a lake, in our state of 10,000 lakes. Even if your children were strong swimmers for their ages, you wouldn't leave them alone by any beach, lake or ocean, swim vest or not. You will need to set a firm rule of no touching the water unless you, or other designated responsible adult, is there. And then be prepared to spend a lot of your time on the beach!

Anything over SPF 50 is a waste, as you need to reapply after swimming, or sweating, anyway. I'd bring both lotion and spray-on types. The roll-on type works well for faces. Vaseline or similar for lips. Floppy sun hats are also a great idea for when playing in the sand or watching children at the beach.
I would bring sand shovels and toys, for sure.

I'd figure out how meals are going to be handled ahead of time. Decide if breakfast is a real cooked meal or if there are just breakfast things available. Same with lunch. Sandwich makings, fruit, snacks can stand for most lunches. Dinners could be the family gathering. Each family could handle a meal with another doing clean up, for example. I'm not usually a "spreadsheet person", but when at family gatherings, a list or spreadsheet can be handy to be prepared and not have to deal with misunderstandings or disagreements during the vacation.

Then mostly, Enjoy! And make great family memories for you and your kids.

Buy them swim shirts so you don't have to put sun screen on their upper bodies. Get yourself one too!

Float vests are dangerous because they give you a false sense of security. Unlike a pool, the ocean is rough. You will need to hold to hold on to your kids if they aren't on the beach.

Bring lots of shovels, etc. and I suggest one container of indoor toys or activities for rainy days.

We prefer to do long drives at night, but I know night driving isn't for everyone.

As far as the cabin, get the info from whoever booked the house. Most of these places are listed on a website with photos, links and local information, so that should answer a lot of your questions.
I have no idea what the ocean is like where you are going. If it's calm, shallow and warm it should be easy with little ones. Here In Northern California most of our beaches have strong currents, the water if fairly dangerous and cold so we don't swim at all, we just enjoy long walks, relaxing and playing in the sand.
As far as the drive, leave as early as possible in the morning, like 4:00 am. I know that's WAY early but you'll have a few hours of darkness and the kids should sleep for most of that (just scoop them out of bed and put them into their seats in their PJs.) This was a lifesaver on our long drives from Nor Cal to AZ when the kids were little.

okay - in New England a beach doesn't necessarily mean "OCEAN" - the beach can be a big lake with sandy shores. So check out just WHERE you will be going - Maine is chock full of lakes.

Maine is hot and humid in the summer.

Plan to bring two outfits a day - two swimming suits and several towels. Most of the cabins I have been to have clothes lines to dry things out. One or two have had washing machines/dryers - so that helped out a LOT.

Find out what amenities the cabin has - full kitchen with pots, pans, dishes, etc. and if not - who is responsible for bringing what. Sheets, pillows, towels, etc. All of this you need to know well in advance. You don't want to get there and find out you need to go buy stuff.

The travel to and from? Plan the route. Stop every two hours, let the kids run, go to the bathroom, eat, etc. Ohio to Maine is roughly 12 to 14 hours depending upon how fast you drive, etc. When I did road trips with my kids? I left EARLY in the AM drove as far as I could with them asleep and then started stopping every 2 hours when they woke up. It's best for EVERYONE to stop and get out every two hours.

Have a GPS for back up.
Pack the car the night before you are going to leave.
have a check list for each person - towels, bathing suits, sunscreen, clothing, tooth brush, etc.
check list for the car - oil changed, tires properly inflated, ac working, cleaned out and ready for a long drive
Gas tank filled the night before as well.

I am not sure what people are talking about with life vests in the ocean. When I was a lifeguard, people didn't allow their children in the Pacific ocean with one on unless they were in a boat. Parents who had children under 3 were with them all the time.

Hope you have fun!!

does the cabin have a washer/dryer? if yes, you pack 3 outfits each. does it supply towels/sheets etc? if yes, done deal.
as for swimming, i think your youngest will be fine getting her feet wet. don't see her or your son for that matter doing much swimming. my kids are 8 and good swimmers yet swimming in the ocean they don't bother much.