Questions & Answers about बच्चे को आग से डर है।
Because को is a postposition, and nouns change into the oblique form before postpositions.
- Dictionary form: बच्चा = child
- Oblique singular: बच्चे
- So: बच्चे को = to the child
This is a very common pattern with masculine nouns ending in -ा:
- लड़का → लड़के को
- कुत्ता → कुत्ते को
- बच्चा → बच्चे को
So बच्चा को is not correct standard Hindi.
Here it is singular.
That can confuse learners, because बच्चे can also be a plural form in other contexts. But in this sentence, को tells you it is the oblique singular of बच्चा.
Compare:
- बच्चा आया। = The child came.
- बच्चे को डर है। = The child is afraid.
If it were plural, you would usually get:
- बच्चों को आग से डर है। = The children are afraid of fire.
So बच्चे को clearly means to the child.