Who is the Child and Who is the parent

So I am left speechless,

Nathan and Katelyn are playing together in the choo choo room, I could hear Nathan say "Dad, look at what Katelyn did". He walks into the office and says, " mommy come see what Katelyn just did.  I fix it, she breaks it, I fix it, she breaks it, I can't keep fixing it."

I start laughing, to myself of course.  I can see that Katelyn is intrigued with the smaller legos that Nathan has.  He build a space shuttle and a Fire truck.

Nathan says to Katelyn, "You see, um um um....."

LOL who says um um um.

Than he looks at me and asked, Are you still mad?  I asked Nathan," who says I was mad". He replies, "Well you did your face, you had an angry face and went into your room stopping your feet" HAHAHAHAHA.

Who is the child and who is the parent?  

I admit I must have had a tantrum.