Such young characters is an issue with a live-action movie, since Gregor and Luxa age less than a year and a half. I'd be annoyed to see 14-year old actors turning 18/19 because of how long it takes to make each movie. Plus Boots would work better in animation, with a voice actor.

I personally think if they were just going to do 1-5 being each book 1 whole movie it should be Live-Action but if they were to make more then 1 movie for each book then definitely animated plus that would be easier and there can be a whole tv show on it or something!