I was there 3 years ago, with girls almost the same ages.
Yes, I agree, you’ve only been dating a month. It’s too early to meet the girls. Make sure that the two of you have a stable, long term relationship before meeting the girls.
I would tell him something like: we need to get to know each other better so that we’ve got some history. That will make the girls more relaxed because we’ll be relaxed with each other. (And mental health experts will suggest waiting months, even a year before meeting the children. They go thru a lot of turmoil if they meet girlfriend after girlfriend.)
You’ll know when you want to meet them. You’ll enjoy all the stories about them, think about meeting them with excitement.
Take your time, and encourage him to take (more) time.
Good luck.