My four year-old girl has started hiding things from me and am worried that she would soon start keeping secrets. What should I do?

Do introspect why does your daughter hide things from you? Do you scold her a lot when you catch her telling lies? Do you impose a lot of restrictions on her? Children tend to lie when they are curious and are stopped or scolded for doing certain things. Just have a nice chat with your little girl and tell her that nobody likes a liar and that mommy gets really sad when she lies. Do not scold her if you catch her lying, simply talk it out.