[David L.]

On our return way, I saw an injured person.

This merely refers to the fact that your eyes are working - you can see objects and people - and happen to mention, of all that your eyes see, what caught your attention.

On our return way, I looked at an injured person

to 'look' is to actively direct your gaze at something in particular.

I saw an injured person and walked up to him for a closer look.

to 'look at' means to examine, as in:
"...and a doctor was called to take a look at the injured man."
"Hey, take a look at this! I just found it on the beach."

"twitter" : this is a repeated sound that a bird makes in a light quavering kind of way. Imagine a bird making a 'tweet tweet tweet ' sound quickly. A bird 'cry' is a loud characteristic call that birds of a species make. A crow's cry is CAW... CAW !
I'm not a bird watcher, but I think they twitter at any time during the day when they are just perched in trees, rather than flying out about looking for food.
'kid' borders on being slang, and is not appropriate to use in your essay account.
a child would be 5 - 11 approximately. By saying young child, we understand that the child is about 5 to 8 years old.
For under 1, words like 'newborn' 'baby'
For children 1 to 5 years, we have words like 'infant' 'tot' 'toddler' 'preschooler'