Please capitalize where necessary: check, before the child travels, the requirements of the country you are travelling both from and to:
A: Check, before the child travels, the requirements of the country you are travelling both from and to:

Q: which means it's yours, theirs and the guest's.

A: Which means it's yours, theirs AND the guest's.

Q: before you can open a avd file, you'll need to figure out what kind of file the avd file extension refers to.
A: Before you can open a AVD file, you'll need to figure out what kind of file the AVD file extension refers to.

Problem: he traveled through mexico to the united states, where president thomas jefferson gave him an honorable reception.
Can you repeat this sentence, but capitalize it?
Answer: He traveled through Mexico to the United States, where President Thomas Jefferson gave him an honorable reception.

Text: in this specific case, poland notified the full transposition of the renewable energy directive on 29 january 2015.

Correct capitalization: In this specific case, Poland notified the full transposition of the Renewable Energy Directive on 29 January 2015.

Problem: once upon a time there was this girl, she was 11 years old.
Can you repeat this sentence, but capitalize it?
Answer:
Once upon a time there was this girl, she was 11 years old.