This isn't social contract theory. Propagation and continuation of the social contract as an end in itself is a value you have assumed.
You skipped between other's children and your own here. If they are an extension of your being, like property and animals, then you can abuse your own as you see fit.
I do not see where this value comes from.
Then the existing theory is too limited and needs revision. A driving principle should be that the social contract is able to continue to exist, which means keeping rational thinkers around. If children are omitted, we can freely cause our own extinction as we can just kill whatever kids we want without violating the contract.
So "tearing up" this contract should also be disallowed.
As an extension of us, but not entirely us, children ought to be included. They are provisional or possible members. As the possibility it may have been us or our children, the mentally enfeebled are included.
We would be primitive in our morality when meeting an alien race and then agreeing not to kill them, but then committing infanticide under the claim that their offspring are not as rational as the adults.
Those who are currently not included in the social contract are trained to do be in it. We raise our children accordingly and provide assistance to the mentally disabled to do so.
To a small degree, this is extended towards dogs. They must poo in designated areas, not attack other humans or dogs, and so forth. They've evolved alongside humans long enough to have a predisposition to work with us so they are.......shall we say clauses in the social contract?
I wouldn't go hunt someone's pit bull for food under the provision that they have trained their companion to abide by the minor clauses of the contract to the degree of feigned membership. Dogs do reciprocate in their own way, what humans do to them and return acts of kindness.
Any animal capable of this, should also be consideration. A chimpanzee that speaks with sign language. Pet cats. And whatever other animal can be trained or almost nearly understand the reciprocity humans possess.
Think of it as a temporary pass to a military installation as opposed to a military issued ID card. Children have the pass until they are adults and have the full on ID. Animals will forever have the temporary pass until revoked.