This is old-school but in my pre-teen years i was reading EE "Doc" Smith's "Lensman" series. It is sugary pulp to me now now but back then it was magic. "Space Cadet", "The Moon is a Harsh Mistress", "Starship Troopers". These days letting them start wading through the "Honor Harrington" books would prolly be good. Most of these are coming-of-age stories and that is often good for pre-teens.
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This is old-school but in my pre-teen years i was reading EE "Doc" Smith's "Lensman" series. It is sugary pulp to me now now but back then it was magic. "Space Cadet", "The Moon is a Harsh Mistress", "Starship Troopers". These days letting them start wading through the "Honor Harrington" books would prolly be good. Most of these are coming-of-age stories and that is often good for pre-teens.