I'm mad at my parents for letting my 2 year old sister damage my computer on their watch
How will this effect the relationship with your parents?
I'm going to avoid my parents by going out for a couple of days
It is understandable to be upset with your parents for not doing a good job watching your sister. She could have gotten hurt and she did damage your computer.
It's okay, since I can go to school, it makes it easier to avoid them.
After you have taken time to cool down, you can let them know what upset you and work on how to prevent it in the future.