Great sentence! Here is a clearer way to say it for kids:
Fennec foxes and jerboas have furry feet so the hot sand won't burn them.
Why this is better (short and simple):
- Furry feet is clearer than "furry socks" because animals do not wear socks; they have fur on their feet.
- So the hot sand won't burn them tells why they have furry feet — it keeps their feet safe from the hot sand.
Another short option: Fennec foxes and jerboas have fur on their feet to protect them from hot sand.
Nice work — you can say either one!