Parenting with preteens

Why does parenting get harder as the kids grow up? I thought the whole newborn thing was hard. Waking up every 2 hours, feeding, diapering, crying, etc. Boy was I wrong! My 12 year old and 10 year old are my hardest I think sometimes. I mean my two year old gets into everything and you cant take your eyes off her. My four year old is stingy and throws tantrums and is just mean sometimes. My 6 year old is whiny like all the time. My 8 year old is sneaky and is whiny when you try to correct her. My 10 year old is whiny, mean, thinks he is the boss, yells, screams, throws tantrums, hits and threatens and fights all the time with his sisters. My 12 year old Tops them all with sneakiness, lying, calling others names, fighting and arguing, thinks she is always right and you are wrong, blames everyone else, screams, back talks, disobeys rules, etc.

I thought I was a good parent. I have rules, I help them with their homework, I reward them, I let them be kids but I am picky when it comes to little things. They have to clean their room once a week and help around the house when I need help. They eat what they get that's that. I do not let them walk to friends houses or go to stores alone with friends. I don't let my kids stay home alone. They don't have cell phones. They don't play on the computer unless they tell me the site they are going to and I type it in and I keep a eye on them while they are on the computer. They aren't allow facebook accounts. My oldest has a email address but that is it. I guess its because I watch the news and the world has changed alot since I was a kid. Its not safe anymore! I want my kids to be kids and not grow up so fast. I see 1st and 2nd graders with cell phones. I hear 4th and 5th graders using foul languages. I have seen 3rd and 4th graders with facebook accounts. I see what the high schoolers do and wear and see. I don't like any of it. I am not ready for my kids to turn into that. I want them to be kind, considerate, helpful, thoughtful, teenagers that use their brains and realize when they aren't ready for stuff and not getting into the wrong crowds. I know they learn from their mistakes but kidnapping, rapes, child molestation, drugs, suicides are all on the rise and I am trying to teach my kids right. My 12 year old got grounded today for not letting me know where she was going and that she was walking with her friend to her house. She told me she was getting picked up to go play and here they were walking around the neighbor hood. Two 12 year old girls alone on a busy street I don't think so. Now she is mad since I grounded her for a week from treats and phone calls from friends and playing with friends. I don't think I am being harsh but I was scared when I didn't know where she was for around 45 minutes. I guess I am just not ready for my kids to grow up. I am just not good at disciplining them either but I want rules followed and I want them to do the right things and stop fighting and whining. Is that too much to ask???