From Great Britain No.
Elsewhere then probably
Yes, children need a passport to enter Canada.
British subjects do not need a passport to enter Ireland if they are arriving directly from the United Kingdom, but you may need your passport for your airline, travel company etc and should check beforehand
Yes they do.
You can enter the US without it only if you have other proof of your citizenship and identity. If not, you need your passport.
That will depend on things like your nationality. Some people would need one and may even need a visa and other people wouldn't. There is no single answer.
If you are not a citizen of the EU you need a passport to enter Spain.
no you need a passport
Yes, they definitely need a passport to legally enter the United States.
Yes you need passport with visa to enter any other country.
Yes, a child needs a passport to enter Canada.
Yes, children under 16 do need a visa to enter Kenya. They are required to have a visa in their passport, and upon arrival in Kenya, immigration officials will stamp their passport with the appropriate visa.
Yes, children need a passport to travel to Mexico.