O que significa "to have a finger in the pie"?

Imagine your son was told to prepare a science project in order to join a contest from his school. It's an annual event that engages the students and even their parents to come up with the best piece of art. At the same time you want your son to make it all on his own, you don't want him to lose the contest. So in order to make sure he's going to do well, you end up getting involved and putting your influence over most aspects of his project. The problem is that your son doesn't like it when you turn into this unwelcome competitive intruder. He says you always want to have a finger in every pie.

What did he mean by to have a finger in every pie? You can imagine what an intruse act it would be someone having a finger in your pie, both literally and figuratively speaking, right? If you hear someone saying that expression, it means they're very intruse and do things in a way that other people do not approve.