This is really up to you. I don't see why you can't be Mrs. so and so, even with your maiden name. You are technically a MRS because you are married. I don't like being called Mrs. ____, because when I hear that name I think of my mother in law, not me. Most of my kids' friends are allowed to call me by my first name -- some call me Mom, because that's what their best buddy calls me. Of course, to get to that point, they probably have hung around your house a whole lot. A friend of mine at church is called "Momma __________" by almost all the teens in church. She mothers all of them, so it's natural.
When my sister and I had our first kids, we talked about what the kids would call us -- and we both felt that using Aunt ____ sounded WAY Too old for us ! So we dropped the title and just used our first names with our nieces and nephews. And it felt just fine, so I always used that with other kids, too.
I had one teen in youth group, however, who called me by my first name like everyone else, and his dad hit the roof. So he was REQUIRED to call me Mrs. ______. I settled that score by calling him Mr. ____________, at age 14. It became a joke between us, and his dad got a kick out of it.
I think what's important is no so much WHAT they call you, but the relationships you build. If you act like an adult and are faithful and respectful, firm and understanding, you will be treated with respect even if they call you tweetiepie.
So find a name and/or title that suits you, and that you will enjoy responding to. Because hopefully these friends of your children will be around and underfoot and you will enjoy them as much as they enjoy you and your children !