Bit of an age range isn't it? 5-10, thats effectively Kindergarten to nearly middle school. Finding material that will work for that age range will be seriously hard. Most professionals I know would not perform for such a large gap.
In my experience, finding material (i.e., tricks) for such a situation is not that hard. For me, as well as other children's magicians who typically perform for entire schools at once, the scenario of performing for an age range like 5-10 is common, at least in North America. Performing for entire schools at once rather than for individual classrooms of kids of the same age is usually what the schools here prefer. School systems and preferences might differ elsewhere, though.
Finding tricks for such situations is easy. Writing effective presentations is the potential challenge.
Look at the work of David Ginn, who performs hundreds of school shows a year for mixed age audiences. That's actually one of the differences you will find with the work of Ginn and Kaye. In Seriously Silly, Kaye explains the differences between kids of different ages and genders and how to play to each distinct group, whereas Ginn's material seems to acknowledge the difference but explains more about how to play to mixed-age groups.
This is also one of the things that makes doing kids birthday shows potentially much different from doing school shows. At birthday parties, you are much more likely to be performing for kids of the same or similar age than at a school show because the birthday crowd often will consist of kids of the same or similar age as the birthday child; there might be a few older or younger siblings or cousins or whatever and, of course, adults, but these are not necessarily the focus of the party. In that regard, it's easier to do birthday parties than school shows, provided you properly acknowledge age & gender differences in the first place.