American Airlines Seating?

Booked a flight and the seats are scattered about the plane. My wife and I don't want my 5 year old son sitting alone for obvious reasons. There are no other seats available except for Main Cabin Extra for 65$ per ticket. Should I pay the extra to be together or wait to see if more equivalent seats open up?

Flights these days tend to be pretty full. You may be able to check and see how many seats are available. But there's a good chance they'll be pretty full, which means you'll have to rely upon the kindness of strangers to allow you to trade seats so you can sit together. There's no guarantee this will work out. I've seen flights where it seems like half the plane is trying to trade seats so groups can be together, and it doesn't always work due to odd distributions. Given the circumstances, I'd pay extra to be sure.

Usually someone will move to accommodate you.

Usually when you get to the gate, you can tell them your situation and they'll make an announcement asking if the person sitting next to you, your wife, or your son are willing to trade seats so you can be next to them. Or maybe there's a couple sitting together willing to trade seats with you and your son so you two can be together. It's obviously not 100% for sure going to happen but they usually try their best to find someone to trade with you and there's usually at least one person kind enough to trade seats.

You call the airline and speak to someone who can get you 3 seats together or the child and one adult.

Then when you get to do the check in you make sure the seats haven't been changed. They WILL accommodate you

You should pay the money for either you or your wife to sit with your 5yr old. Don't play the waiting game, then you will be one of those obnoxious people that gets on board expecting people to move around to accommodate your cheapness.

Pay the extra

You can wait. Don't select any seats how.
The airline will change the sitting to allow you and/or your wife to sit with the child.

If you want to handle it sooner rather than later, call the airline after you book the ticket.

Call the airline. They can very likely work something out for you in advance.

If not, keep an eye on the seating. As it gets closer to your travel date, you'll often see that the seating availability shifts a bit.

The airline will move people around to ensure that at least one of you is next to your 5yo.

Should I pay the extra to be together or wait to see if more equivalent seats open up?
Doubtful any pairs will open up.
You get the assistance of a human at the Airline to assist you. They could have done this at the time of booking. Remember that for next time.
As you booked the cheaper middle seats some other passenger you now expect to just give up their premium window or aisle seat. Many now demand some compensation. Some are more friendly and will switch.

You knew this the minute you booked. NEXT TIME get this figured out at time of booking. There's a reason they still employee humans in the reservations office to assist passengers with making a booking with some special need in it.
This is also one reason there are still travel Agents to handle a situation like this.
You have been honest and have said you only NEED two together and not all 3 much easier to get done.
YOU DO NOT HAVE TO DO IT YOURSELF ONLINE.

Cheap Bargain Basement, lowest price is not for all situations.Sometimes you just pay a little more to make it easier for your travel group and the others on board that want the seat they want and booked.
The sooner you contact the Airline the better it is.
The bargain web site IS NOT THE AIRLINE

The recent fights at boarding time is something you should try to avoid. Sometimes other passenger is not thrilled to change seats.

During the flight the parents could trade with each other to have part of flight with child.

Planes are getting more full than they used to be. The window seat and Aisle seat are premium priced as passengers are willing to pay extra for them.
Seat together can be arranged at time of booking. DO NOT expect cheap price on all the seats in a row,

Enjoy your flight. The longer you wait the more hassles for others to accomadate your needs.

Many HUMANS at the Airline can assist you NOW one less thing to deal with on travel day.