What are some of the bad habits which affect kids' (3-8 yrs) eyesight? How can parents ensure good eyesight for children.

I think frequent use of gadgets. Based on my experience, I witnessed how my little sister grew up. Almost all day she's infront of the computer since she was a baby. She now has a bad eyesight with very high grade lenses unfortunately. Another thing is that she can't stop her habit being infront of her gadgets the whole day.