I want to order food and send it to someone else's table
Why do you want to order food for other people?
They just look like a friendly family, so I want to do something nice for them.
It's nice to order something special for a family that are sitting at another table. However, you should let the waiter ask if they are interested before the restaurant prepares something and brings it out.
I'll ask the waiter about that.
Well this is nice of you to do, I hope they enjoy their free meal!