I bet you could really enjoy the tree and it's ability to provide you with shade by adding a tree-house and tire swing. Think about how much fun you could have if a slide went down from that tree. You could keep us posted on how the project is going too.

Where the two trunks are joined that is called co-dominant leaders. The dark area between them is rotting between the two trunks . This is a far greater danger. The upper tree limbs removed left huge scars the damage has healed never cover or fill . The tree can heal on it own .
The co-dominant trunks touching is a far greater danger . The trees trunks where they are touching are slowly rotting and will eventually weaken and rot out until the tree gives way and falls. There is no air or sun or space for the trunks to grow . There is no way to protect the co leader trunks touching and no possible way to heal. It will continue to rot as the tree continues to grow and becomes heavier and at higher risk for rotting and creates conditions susceptible to fungus and disease . The area will continue to be a risk of falling due to existing rot and decay until the tree is either removed or falls.

I am not a tree arborist. Call a tree specialist to analyze the tree for a closer professional evaluation.

@bumplbea - I wonder if it would help to cable those two trunks together? I will tell my son to call someone. There were ants and some debris in that crook, so I agree it is a weak spot. We took care of the ants and debris, and have been checking it monthly to make sure they do not return, but yes, we should have an arborist look at it - thanks.

@PacificPonds - my son has a newborn and is already planning a tree house. A swing would be nice to - maybe I will get my grandson one of those baby swings!

cwhitt I am so glad to hear that you are aware of the danger that co dominant trees represent. By the time your grandchild is old enough for a tree house the tree could be degraded much more. Once the fungus is in the tree there is no cure. I have cabled a few trees in the past and it is only a temporary fix. The tree is constantly growing and the rotted area will only get bigger as the tree gets larger and heavier.

Cables? It will be constant cabling as the tree grows and the weight of the tree continues to shift. The co-dominant area is very low to the ground . By adding a swing and a treehouse will add more weight and movement/pressure to a already diseased/risky tree . Leaving the tree as is is of course your decision.

Have you tried calling a certified arborist for a qualified opinion, and you would have the peace of mind on what is best in your case.
Or ..Plant a larger ...15' tree now and then you will have a safer alternative for this grand child and more to come in the future.

More info from arborist in Oregon - dangers of co-dominant trees.
https://youtu.be/9dDcdsskuN0