Five short rephrasings for a 7-year-old
The walrus uses its tusks to climb onto the ice and protect itself.
With its tusks, the walrus climbs onto the ice and defends itself.
The walrus climbs up the ice and defends itself with its sharp tusks.
Using its tusks, the walrus climbs onto the ice and stays safe.
The walrus uses tusks to get onto the ice and keep itself defended.