The best approach is to honestly tell them exactly what you want:
However, they will obviously be concerned for a couple of reasons (you haven't done this before, and they like control, being 2 obvious reasons), so you should come to the conversation prepared to address those concerns.
Being prepared would actually act as two independent pluses in your favor: first, because it will address the concerns. Second, because you being prepared will show them that you're thoughtful and mature enough to think things through.
(As a matter of fact, you may want to honestly come out and initiate that part yourself, telling them "I know you guys probably have some questions and concerns, here's what I prepared to address them". This would show them that you are both mature enough to prepare AND that you're concerned enough about their feelings and thoughts - both likely to be pluses in their minds).
What could be those concerns? Well, it's hard to know 100% sure without knowing more specifics, but be prepared for them to be interested in:
What are specific plans that you and your friends have for when meeting?
Obviously, if you have specific plans you can elaborate on, it will be far more calming to your parents.
What kind of people are those friends? Are they from similar backgrounds to yours? (introverted, value learning).
Why have you not told them about the friends before?
You don't need to lie or make big story on this one. Just honestly admit that because of your past lack of experience, you were worried that your parents may be unhappy. Or that you were too shy to discuss the topic.
What kind of households do they live in?
Are their parents someone who'd take as good care of them as yours do?
Do the house rules differ in meaningful ways? (e.g. a concern your parents may have would be if the friend's parents allow things that your parent's don't allow you - from drinking to drugs to adult entertainment). A 9th grade, some households are more relaxed about things like that than others.
Depending on your parents, they may want to know if the households are similar culturally (e.g. if your parents are religious and observant, they might feel better if the house you're visiting follows similarly).
Bonus points to earn
As a parent (though younger kids than you) I always want to talk to parents of the kids if there are visits involved, beforehand. So, if you arrange with your friends to have the parents talk to each other, your parents are likely to appreciate that.
Nothing fancy is needed - just get the friend's phone#/email, and ask them to let their parents know in advance that your parents might call to discuss the visit and why.