This is the time of year when many Americans apply for their passports —  either new or renewal.

But there are a few things you need to know. While your U.S. passport has a validity of 10 years, childrens’ passports expire in five.

But don’t wait until the last minute to renew your passport. A growing number of countries insist that a passport be valid between three to six months after your arrival there.

If it isn’t, you may be denied entry.

Also, for frequent flyers, another caution: some countries, like South Africa, require a number of blank pages to stamp entry visas. And the U.S. no longer allows you to add new pages. So if you’re running low on passport pages, you may need to get a new one… and soon.