Perhaps Percy Jackson would be a better beginner movie but it may be a bit intense for eight. Are there any elementary friendly ancient history movies? Could there be?
Percy Jackson is completely fine for an 8 year old boy... just action that they would enjoy seeing and will keep them engaged (nothing too violent.. no blood - just "magic"). Whatever they pick up from the mythology is a bonus. Anything else would be over their head - which is fine.
That's the bloody problem with this forum......too many likable, lovely, generous, anonymous, caring, folks. Almost scares the hell out o' ya, don't it?
For family friendly I would go to the oldies but goodies: Ben Hur, Quo Vadis, the famous 1963 Cleopatra. Been a while since I saw any of those, but I think everything from back then can be considered safe today. Personally I would go with Cleopatra - stunning.... SC