That's wonderful to hear that you have a passion for animals at such a young age! Here's a possible way to fill in the blanks in your text:
I'm only ten, but I know what I am going to be in the future. I love animals, and I want to be a vet. I want to treat animals. I have two pets: a dog and a parrot. I take care of them. My little sister Alice is two years younger than I am. She often helps me. She feeds the pets and likes to treat different animals. Last summer, I went to my grandpa's house in the country. I helped him with the cow and chickens. I enjoyed it very much.
Great job expressing your love for animals! Good luck with your future as a vet!