"Het kind loopt de straat op, zonder te kijken."
Translation:The child walks onto the street, without looking.
That means "The child is walking on the street." Het kind loopt de straat op means the child is walking onto the street from, say, the sidewalk or a driveway. In other words, the child wasn't on the street before. Imagine a child playing with a ball when it rolls onto the street and now the child is chasing it and not watching out for approaching vehicles.
Well, you need a preposition, just like in English. And when "in", "op" or "uit" are used to specify a direction of motion, they are usually placed behind the noun. See Dutchesse's post above. Another example:
- Ik loop de kamer in. = I am walking into the room. (direction of motion)
- Ik loop in de kamer. = I am walking inside of the room. (location of action)