My family stayed in this Acadia Sunrise motel about 15 minutes drive away from the town of Bar Harbor. The motel has a pool and is pet-friendly.
https://www.acadiasunrisemotel.com/
Our visit was about 15 years ago but I thought the motel was perfectly fine as a base to drive into the town and into the park for day sightseeing. It is not in Bar Harbor.
We spent time at the Bar looking at the sands at low tide, went whale watching, shopped in the town, drove into the park and up Cadillac Mountain, did some other things more for little kids.