Having Kids Costs a Fortune.

Having children costs a fortune

I had a smallbrief talk with my workmate just now.

After calculating the costs, we thought that we could be happy girls with no children.

We discussedtalked about the expenses of getting married and raising children.

Another way of putting it.

I had a small talkbrief conversation with my workmate just now.

"Small talk" usually means short conversations that are mostly insubstantial. For example, talking about the weather or a trending article is considered small talk.

After calculating, we thoughtconcluded that we could just be happy girls with no children.

I had a small talk with my workmate just now.

"I was having some small talk with my workmate just now."
or
"I was making small talk with my workmate just now."

It doesn't matter but if you'd like to know, in American English we'd say coworker instead of workmate.

After calculating, we thought that we could be happy girls with no children.

There's nothing wrong with using the word girl here.. but nowadays it's the general trend to say women when you mean adult female (I'm assuming you're an adult).
"Girls" here is totally fine though. The difference in meaning would be that your coworker is a very close friend, like almost a sister.