Need help about seat selection for family with toddler

I'm planning on flying from DC to Hawaii to visit my grandma who is 100 years old with my husband and toddler who will be around 18 months by then. This will likely be our first trip on a plane.

I wanted some second opinions from other parents who have traveled with small children.

The best itinerary I've seen is a direct flight but the plane body is 2, 3, 2. And I want to book my son his own seat even though I know he can sit on my lap under 2. It's such a long flight I feel like we need more space.

Should I book the 2 person window aisle and have the other parent sit in the adjacent row? And have the parents rotate sitting with the toddler? This is tempting in that I can get my husband to sit with my son the whole time lol.

Or should I book the 3 person row in the middle of the plane without a window? Is it possible to contain a toddler in the middle section with parents on both sides?

Thank you!