K.L.
I see others have suggested having the parents over to your home or meeting out for coffee, tea, etc. But, this doesn't really give you a sense of their home atmosphere. Since all parents have (or need to have) this concern, you might contact all the families and suggest that you all take advantage of your children's new friendships and plan an activity that will help all the families get to know each other. I would just be careful to not take on the attitude that you need to investigate them. But rather, suggest that you welcome the opportunity to develop community relationships with other community-minded families or that you feel it would help the children feel more secure about their new friendships if the parents all got together. One idea I've seen work beautifully is to plan a progressive dinner. Take a Saturday or Sunday afternoon and have appetizers at one house, salad at another, sides at the next, a main course at one house, and desert at yet another. It takes some planning, but it can be great fun. This way, you can get to know the whole families a bit better and you may just make new friends yourself! But, keep your focus on developing friendships naturally. No one is comfortable if they sense they are being looked over to see if they are 'safe'.
If you are limitted to a phone conversation, you might just say that you want to help your daughter be prepaired for a sleep over. Tell them that you know each family has their own 'family culture' and that you want your daughter to know how to conduct herself respectfully. Then you can ask very specific questions about everything from foods your daughter may not be familiar with and if she will be expected to eat whatever is served to whether or not she needs to be aware of anyone's special needs. This will also give you an opportunity to explain any special needs your daughter may have. I know, as a parent, I would have welcomed such a thoughtful call from another parent. You can even offer to help with the sleep over. Offer to bring a dish or help facilitate some game time, a special craft project, or storytelling, to make it a special event and give the hosting parent some support. You can also suggest that if they need someone to run to the store for something, they can call you. Being helpful is a great ice-breaker!
However much we might try to know the families and know how our children are being watched, or not, there is only so much we can control as parents. One of the best things you can do is to talk things over with your daughter and let her know she can call you to come get her if she is faced with something too awkward or uncomfortable. You can make a plan for her to make a graceful exit. For example, you could tell her that if she needs to call, she can simply say that she forgot to tell her mother something important (like a phone message) or has a question and needs to call. She may not have the opportunity to talk on the phone privately, so give her a code word she can use on the phone that means she wants you to come and get her. Then you can ask her to give the phone to a parent and tell them you have a minor family emergency and will need to come and pick up your daughter. I remember my 11 year old son spending the night with a good family. Some of their standards were different from ours, but they were conscientious parents. But, once an older cousin came to spend the night while my son was sleeping over and that cousin brought an X-rated video he had gotten his hands on. My son came home asking me some truly unexpected questions!! Although I was disappointed that the boys were not better supervised, I was so glad my son knew to come to me with those questions. We were able to talk about it in a way that helped him develop a healthy sense of respect and honor toward women and sexuality.
Your daughter is at the age where it becomes increasingly difficult to try to control what they are exposed to. The one thing I did not want my son to have was a worrisome mother. So, I did my best to know my son and make sure he knew we were available and accessible and to prepare him to handle himself with dignity. And, most importantly, I prayed!!! I learned to remind myself that this is God's child that I was caring for and that we are all just as much in God's hands as we were the day we were born.
My son once told me that he was reminded how much I prayed for him when he was a teenager because he could not seem to get away with things the other kids did. He said it was uncanny how, if he even thought about crossing a boundary, something would happen to make it almost impossible. He would get caught before he had a chance to do something really stupid. However frustrating this may have been for him in some ways, it always proved to him how much he was loved. To be honest, I don't know how parents raise children without prayer. There is just too much that is not under a parent's control.
I hope you don't mind if I share the prayer I carry in my heart for my son. He found this prayer when he was 7 y/o and he decided to memorize it. I thought that was so precious, so I memorized it and still recite this prayer on his behalf every day. At times when I was most prone to worry about him, this prayer was my rock:
O Lord! Make this youth radiant, and confer Thy bounty upon this poor creature. Bestow upon him knowledge, grant him added strength at the break of every morn and guard him within the shelter of Thy protection so that he may be freed from error, may devote himself to the service of Thy Cause, may guide the wayward, lead the hapless, free the captives and awaken the heedless, that all may be blessed with Thy remembrance and praise. Thou art the Mighty and the Powerful.
- 'Abdu'l-Bahá