Why do Catholics Bless Themselves?

Holy Water Font

The question took me by surprise.  I hesitated a minute before answering the little boy.  I said,
"I say in the name of Father, the Son, and the Holy Spirit, while I dip my fingers in the holy water.  The prayer and the water are to remind me of my Baptism.  The reminds me that I am a child of God."

He didn't say anything.  He just ran over to his mother.

I think I answered his question in a way he could understand.  Just to make sure, I asked my Google app, "Why do Catholics bless themselves with holy water?"

My iphone answered back,  "People have religion.  iPhones have silicon."