<p>For all the OP knows, since the other family did the inviting, they actually may be planning to treat everyone. If so, that will become evident if they offer to pick up the bill. If they do, then the OP should let them pay. Otherwise, split the bill.</p>
<p>They may have offered the invitation in hopes that the OP’s family would be willing to do things like be kind to their daughter since the D will be in college so far from home. They also may be planning to treat because they know that it’s possible the OP’s family will do things to help their D that the parents and D won’t get a chance to reciprocate.</p>
<p>For instance, my S has stored things at his local roommate’s home over the summer, and S also spent about a month with them after school ended when S was working on a project with his roommate. Other than treating the roommate to a meal, H and I have never been able to reciprocate.</p>