How often do babies and children have to renew their passports? In the
US and in other countries.

Hello, chrisrowe-ga! 


 A U.S passport for a minor 15 years or younger is valid for five years.
 
 A U.S. passort for a minor 16 years or older is valid for ten years.

 See "How long is a passport valid and when should I renew my passport?" 
 http://travel.state.gov/passport/fri/faq/faq_1741.html#valid


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Examples from other countries:


India - Validity of the passport for minors is 5 years from the date
of issue of the passport or the minor completing 15 years of age,
whichever is less.
http://www.mp.nic.in/passport/apply_minor.htm

UK - A child passport is valid for five years. When it runs out you
can renew it for another five years, and so on. If your child is under
16 they cannot apply for an adult passport. For example, a 15-year-old
who needs a passport must apply for a 5-year child passport. They can
use this until it runs out, in this case when the ?child? is 20. When
a child reaches 16 the next passport they apply for once their current
5-year child passport runs out should be a 10-year adult passport.
http://www.passport.gov.uk/passport_child_law.asp

Australia - Children's passports are normally valid for five years. An
Australian citizen under 18 years of age who has never married is
regarded as a child.
https://www.passports.gov.au/Web/newppt/applying_u18.aspx


* Since each country has different requirements, you will need to look
up other government passport agencies individually.


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 I hope this helps!


Sincerely,

umiat

US passports passports are valid for five years for minors.

Paying $5 for information readily available at the State Dept. website
(under passport link).  It's YOUR money......