As a frequent business traveller (and a Dad) I would suggest that you check for seat re-assignment at the gate and see if you can get seats across the aisle from each other.
If that does not work, I can tell you that I have more than once, switched seats out so that families can be together. Don't dispair. I think most people (unfortunately not all) will be more than willing to help you out if you ask nicely. Especially while I am away from my family on a business trip. I find it impossible to keep another family apart even if it is only a few feet apart.