No mainline Assassin's Creed game released on PSP. The closest are:
Generally no. ESRB rates main entries M (17+) / PEGI 18 for:
Bloodlines (PSP) is rated T (Teen) / PEGI 16—still too mature for most 9-year-olds.
Always check ESRB/PEGI ratings, watch gameplay videos, and decide based on your child's maturity.