Can I let my 7-year-old lead me in prayers?

So, according to the overwhelming majority of scholars, a child, somebody who has not reached puberty yet, is not able to lead an adult in Salah. The Salah will not be valid if a child leads an adult. That's according to the majority of scholars. There is a second view, however, it is not the majority view, which is that the Salah would be permissible. However, I would always err on the side of caution, particularly with Salah. It's the most important aspect in your daily life as a Muslim and just be on the safe side and go with the overwhelming majority view that a child is not able to lead an adult.