use of "there is/are"

One usage is exactly as good as the other. Her version indicates that there are two kids at school that you are talking about. Your version indicates that the two kids are somehow connected to you.

We = staff ?

We have two errors in the earlier posts.

There are two errors in the earlier posts.

And now we have more there.

Simple answer is the following: “is” is used for singular and are is used for plural. However, an understanding of which grammatical application is the collective is necessary. A group is considered as a singular entity. Whereas, multiples of individual items (or of a disparate nature) is considered plural

As an an example: The flock has wandered off the paddock.
Whereas: Mary and her sister are tending to the sheep.

"Is" is for 'singular'
"Are" is for "plural"

There is a fish
There are many fish

When there is a thunderstorm
When there are thunderstorms

That is how I use is/are.