In terms of things younger children may struggle with, Naruto is a mixed bag.
Later fights especially may be frustrating to younger children, as chances to heal yourself grow further and further apart, forcing you to take on fresh enemies without the chance to heal your wounds. With gigantic explosions, the ability for some characters to duplicate themselves, and some distinctly fantastical baddies, the fights are suitably spectacular, but can take some getting used to. At its heart, Naruto is a beat 'em up that sees you facing off, mostly one on one, against other characters from the series in battles that are anything but realistic.