Your tween wants to be like you. It's possible that your tween is bossing the younger kids around because you've been a great example. She may look up to you and simply be mimicking your own behavior. This can be a sign that you have been a good example that she wants to follow. At this age, the parent should still be supervising, but the tween can be given some extra responsibilities. Allow your tween to facilitate activities and look out for the welfare of her brothers and sisters. But do not allow her to discipline them.
Your tween has too much responsibility. Having extra responsibility can sometimes be a good thing, as it prepares tweens for babysitting in the future and just life in general. But it also can be a bad thing if your tween is overstepping your boundaries. It's perfectly fine to allow your tween some growing room. But don't let him take it so far that he believes his siblings have to listen to his every word. If you catch your tween trying to boss around brothers and sisters in matters where he shouldn't be, you need to act immediately to rectify it early.
Your tween knows she is older. Trying to take charge can just be a natural instinct as a child grows older. It is particularly present in tweens with younger siblings. This is just the natural order of things. If the manner in which your tween outranks siblings is not significant, there is probably no need for concern. It can actually be good for kids to have an extra reminder for simple things. But if you see your tween take advantage, explain to her when it is and is not appropriate to correct siblings.
She's practicing for the future. Your tween may have natural parental instincts and is acting them out on siblings. There is nothing wrong with this, so long as it isn't hurting anyone or overstepping boundaries. This is how kids learn to be good parents when they grow up. Use this as an opportunity to teach your tween about proper parenting techniques, within reason. Helping with dinner, reading to the younger kids, helping feed the baby, preventing fellow siblings from arguing, and similar activities are great ways for your tween to participate. Just be sure she knows that certain decisions are still up to you.
Take a look at your own habits. Many times, it will just be a natural part of growing up. But sometimes tweens will act this way because of the behavior of the parents. If you let your tween take over one too many times, she will start acting like she's the parent. Instinct takes over and it can be hard to break this habit once it starts. Ideally, you can catch it before it gets out of hand. Otherwise, it will take some work to let your tween know what her true responsibilities are and are not.
*I originally published this via Yahoo Contributor Network