It's fine, though there is a lot of driving around, and most of the highways are not interstates.

There are at least a dozen recent reports on this so I will only hit a few high spots.

I would probably skip Boothbay in favor of a second night in Camden, and I would take a windjammer day trip from there. They usually last about two hours. Drive up the mountain just north of town for incredible views. Rockport, very picturesque, is just south of Camden, and Rockland, much larger, is not far south of that. It has a fun main street with lots of kid friendly places to eat. The Farnsworth Museum is great but so is the working waterfront and the State Park and automobile museum just south of there at Owl's Head.

Portland has great shops and restaurants, cheap and very popular minor league baseball, quaint streets and brew pubs. Guy stuff galore. The best thing is the State Ferry, which runs to various islands so people can commute to work. It is like taking a cruise at bus prices. Lots of routes of different lengths. I would stay two nights and do Old Orchard Beach as a day trip. The less you move around, the more time you will have for fun stuff.

Since you are from Michigan, I will just say that this area is a lot like around Charlevoix and Petoskey. Finally, the good scenery is not on the main road. Explore the side roads to tiny towns like Port Clyde to see the Maine of your dreams.

I would check to see if your visit coincides with Bath's Heritage Days. They have a great parade, craft fair and midway (although we didn't visit the midway).
I agree with drive up Mt Battie. The view is incredible. We take bag chairs along with a picnic lunch and binnoculars. It would be a good break from driving. Several years ago we stayed at a motel/cottage place just north of Camden in Lincolnville. Glenmoor by the Sea. We stayed in a unit that had a separate LR area from the bedroom and a small kitchenette area (fridge and microwave). Although right on Rt 1, it has acres of grass and walkways (plus pool). It's a place where your 5yo could ride a bike while you watched from the deck.
The Botanical Gardens and lobster boat ride will be nice. Boothbay is very crowded.

Owls Head Transportation Museum is a favorite of my husband. Check their weekend schedules because they usually do some extra events. The nearby short hike to Owls Head Light ends up with a great view.

I think staying in Portland and doing a beach as a day trip might be a good suggestion. Our family favors York Beach which has a nice playground near the downtown area. It sort of depends. My husband and I enjoyed the mailboat cruise of Casco Bay but it might be boring for a 5yo. A friend loves Peak's Island but we didn't explore it. If you stay near the York downtown area you can walk to Nubble Light for ice cream. If you want some beach time York is great. In Portland, your husband might enjoy the brewery tour. Friends and I loved the foodie tour but it would be boring for a 5yo. Definitely try the french fries at Duckfat (within walking distance of brewery). We have not been but I believe Portland has a children's museum.

All that said but I also agree with Ackislander that the Maine you probably want to see is down some local road. We usually explore and just drive and drive around usually finding a lobster place for lunch. If you look on a very detailed map you will be able to find an ocean front wildlife preserve where you can enjoy yourselves. Let 5 yo play in the water. Beach might be very rocky and place hard to find but it won't be crowded. OTH places like downtown Camden and Boothbay will be mobbed.

Your iteniery is quite good. The extra one that I would suggest is going to Rockport as the views are amazing there. Botanical Gardens are good too. Portland also has a children's museum, which will be great for your kid. Enjoy!

Your iteniery is quite good. The extra one that I would suggest is going to Rockport as the views are amazing there. Botanical Gardens are good too. Portland also has a children's museum, which will be great for your kid. Enjoy!

If you do decide to do OOB from Portland, it gives you the flexibility for changing days if it is rainy or too cold for the beach. The beach at OOB is beautiful and a kid could be happy building sand castles, body surfing at low tide, looking for shells, there is a strip that goes for several miles with nice white sand. Do keep an eye on her at high tide as there can be an undertow in some places along the way.

In Boothbay there is a small aquarium, I believe it might be called the Maine State Aquarium. It is very small but has an excellent "touch tank", full of lobsters, starfish, sea cucumbers, etc. You are able to pick up everything and lift it out of the water for a close look. Your 5 year old might really like this. My kids loved this when they were younger. There is also a nice picnic area outside and a great view of the town. We also went to the botanical gardens and they are really beautiful but be prepared for a lot of walking. I think we were there for a few hours. One of the reasons we went is there is one section where you can make your own fairy house. There are even building supplies like piles of pinecones, shells, branches, stones, etc. at "Gnome Depot". There are literally over 100 fairy houses already built in the area, the kids loved this section. We have always stayed in the Wells area and liked to go to York better than Old Orchard. A lot of the old shops and amusements in OOB have been torn down for condos. In York it's a much smaller town with an old time feel to it. Have fun planning your trip.