On a family walk the other day, Bram finally clued into this and every minute or so would yell, "k?" and look at me. He would repeat it over and over, "k? K? K? K?" until I would answer in the affirmative that I was indeed okay! I then am required to ask him if he is okay, which he responds to with a very enthused head nod.
Then he has to ask Anders if he is okay. To which Anders often grumpily replies, "No!" Bram doesn't know how to respond to this answer so he will ask Anders again. When he gets a second grumpy, "NO!" I tell Bram, "Say what's the matter?" So Bram will say, "matter?" and is generally satisfied by that point.
This conversation is usually repeated several times until we get Bram distracted with puddles or storm drains.