The Haydn is actually deceptively difficult. Not a good choice for a first timer.

Without knowing your kid and their strengths, it's hard to pick a solo for them. All'Antica by Goeyens is fairly accessible. Andante et Allegro by Ropartz is a good "entry level" Class 1. And Sonata VIII by Corelli is much easier than it appears - very tuneful and lays well, just have to get the style and 12/8 meter for mvts 3 and 4.