Here are three simple ways to say those two sentences for a 6-year-old:
Fennec foxes and jerboas don’t fear the hot sand.
The bottoms of their paws are furry.
Hot sand does not scare fennec foxes and jerboas.
They have fur under their paws.
Fennec foxes and jerboas can walk on hot sand without worry.
The soles of their paws are covered in fur.