You have great responses above. I wanted to add the reason changing age groups may not happen.
If you sell your first picture book to a publisher and the book does well, the publisher might consider turning it into a series. (The term well is relative.) If the series does well, maybe there will be chapter books and even a TV/streaming show. This happens. Picture books and chapter books are read by the same age group: 4-8 year olds. As kids learn to read, they jump back and forth. It's easy to keep the same or a similar tone as well.
I don't know if there are any series that have jumped from PB to MG. (If anyone does, please share.) There are licensed properties, like Star Wars, that are so popular they have work in every age category, even adult. But those are the exception. Even Harry Potter's jump from MG to YA is rare. It strikes me that visual media (movies, etc) may be a necessity for such a marketing boost.
Here's the thing though. If book one doesn't do that great, why would a publisher pick up book two, much less book ten? It wouldn't be good for business. So all of your dreams hinge on that first book.
This isn't to say you can't execute your other ideas. Even if book one fairs poorly, you can change the next book up so it uses new characters in a different world (unless the world is this one) and sell it. Just take it one book at a time.