Thinking they are the boss / Acting Bossy
Before You Begin
Pause and breathe. Even if this shouldn't be happening... accept that it is and embrace it with composure and calmness.
Calmness is the only way forward because without calm, there is no possibility for receptiveness and connection. Your child won't give to you any more than they see from you.
Never forget that a strong connection is fundamental, as there will be no correction in them if there is no connection with you.
The Core Problem
An mix of trying to control the situation to go their way and very likely an unmet need of feeling worthy and important.
What Will Make It Worse
Getting into power struggles will only prolong the situation.
At the same time ignoring the behavior or letting the child be in charge frequently will reinforce his/her belief that they are the boss.
What The Child Needs
1. To feel heard and considered: Oftentimes, letting the child explain what is important to them and showing them that they are being acknowledged in the plan will make them quickly shift from being resistant and controlling to cooperative and accepting.
2. To understanding appropriate leadership opportunities: The child needs to learn about appropriate times for leading a group, such as when there is a problem and no leader already, or when they are best suited to handle the situation based on their relevant experience. Offer examples of opportunities for helpful leadership in various situations.
3. To understand the need for cooperation: Encourage the child to work collaboratively and understand that being a leader often involves being a good team player.
4. To know the boundaries: Discuss boundaries to help the child understand when it's appropriate to take charge and when it's required to follow directions.
How To Have The Conversation With Your Child
Find a place free of distractions where the child will feel comfortable talking freely.
Begin the conversation calmly, expressing that you have noticed the child has been firmly trying to control recent situations, like a parent or a boss. [Provide specific examples if you can - it is really helpful for the next step]
Continue with a tone of curiosity, expressing that you are interested in why they felt they had to step in and take charge in those cases. Actively listen for any clues of their unmet needs, and acknowledge them out loud back to the child. I.e. "I hear that you tried to wait for your turn but it never came, so you took over the game to ensure you got one.
Express genuinely that you support them being a leader and want to help them level up at it. Move on to working through the list of what they need. It doesn't have to be all in one conversation, but make sure your child makes the connection along the way between what you are talking about and preventing unhelpfully asserting themselves as the boss.
Ideally your child comes away from the discussion(s) feeling understood and a having a more mature understanding of when to lead and when to follow.