Answer:
I only exist when you are here. Where you never were I can never be.
I go up and down at the same time. Up towards to sky and down towards the ground
The more you take the more you leave behind. What am I?
What has one head one foot and four legs?
Soft and cuddly I'll pull on your heart. But take my last name and I'll tear you apart.
Give it food and it will live, give it water and it will die.