"They have put on their pants."
Translation:Ils ont mis leur pantalon.
Quirk of French-English translation. I had the same problem studying English. In English, we say They have put on their shirts because there are many shirts (and I was picturing each man putting many layers of shirts), whereas in French, we say Ils ont mis leur chemise because each man has one shirt.
There is no "most logical" rule here, they are just different and you have to get used to it.
In English we say they have put on their pants, because they are more than one [they, their], and because there are more than one, each of those people are putting on pants [plural]. The inquiry was valid, but the explanation wasn't enough to understand the question asked. I also would like to understand how multiple people get into one pair of pants. I thought the plurals had to be in agreement for the phrase to be correct. I have read this page and still haven't seen the answer. We expect French and English to be different- so no problems with that- but we are here to learn and if we still haven't understood, then we haven't learned. I would be very grateful if someone could offer an explanation please (& no offense intended towards anyone).