If you have a beginner trumpeter, you don't want a beginner solo to contain different sections with varied articulations and "slow and pretty" in there. You want them to be able to play beginning to end without falling apart. Add in the other stuff later. They're twelve, not auditioning for a performance at the ITG conference.
There are lots of "easy" beginner solos on the Grade 3 list that are in a book full of like solos. Many of those aren't on the list - and are right up what you should be looking for.
This would be a solo for a student at the end of their beginner band year. Previously, I have used "Country Gardens." I love its technical components, but dislike that it doesn't include a short, contrasting section.