Easy to do split screen:
Load up giddy park with ai.
Make acorn your second controller and the sunflower as your main account.
Place the acorn in the centre of the map near the stairs on the left, as the tv screen zombies regularly run down them. Let them kill the acorn, revive with your sunflower. Press X to revive and hit LB to heal yourself while reviving so you don't go down yourself.
Repeat 10 times and achievement is yours.
Took me less than 10 minutes