Scratch is not far off from growing with you. Back in 2013, I taught a 30-hour summer class for elementary and middle school students aimed at this.

It was bout 20 hours of programming concepts in Scratch, and then 10 hours of transferring their learning of Scratch semantics into Python syntax.

Most of the younger students in the class wanted to keep playing with Scratch, but the older ones intuitively understood they could go far with Python -- and that Scratch was a nice place to test/debug algorithms before implementing the "final" version in Python.