Strange, now (March 20, 2018) I put "Many children are little." and that was not accepted but they gave me the correction as "Many children are small." So, it depends on context. If you said "my little brother" , that would mean "my younger brother" and the German word "klein" only refers to size, not age. They may not accept "little" from the German word "klein" for that reason. I have since found out that “klein” specifically means “short” when talking about people, but means “small” or “little” for things.
I believe that this has been reported and you should try again.
Did you try to report it perhaps put My translation should be accepted?
Still, there are so many ways to say the same thing. I would just say “Many children...”. I think “a lot of” is usually used to replace “much” for quantities that we don’t count and “lots of”. Is used for quantities that we can count and this is one of those. Though ultimately people do use those two interchangeably.
Yes, "small" refers to size, but "little" could refer to size or age and "short" refers to size only about height. A short child could be a short fat child or a short skinny child. A small child would not likely be fat. A big child could be tall or heavy. You would say a thin or skinny child, rather than a small child if he were tall but under weight. You could say "a small fat child", but it would be strange to say "a small skinny child" as it would seem redundant as small covers overall size. You could say it, but you would be emphasizing that the child is very skinny for a small child. The thing is "klein" does mean "small" and sometimes in English we say "little" to mean "small" and often in English we say "small" to mean "short". There is overlap. http://dictionary.reverso.net/german-english/klein
On the other hand, "short" only means "klein" when talking about people. http://dictionary.reverso.net/english-german/short http://dictionary.reverso.net/german-english/kurz
Then there are expressions: "My little sister" would be "my younger sister." "My big brother" would be my older brother." Your little sister could be taller than you and your big brother could be shorter than you. There is no way to know from this expression.
"You are a big girl now." means that you have grown in size over time and are therefore older. You could say this to a child who is still rather small, but they are bigger than they were. This is often flattery used to get a child to act in a better way or to let them know you expect more from them.
“Kurz” does mean short in length, but “klein” is used for height of people. https://dictionary.reverso.net/english-german/A+short+man
No. Those words mean different things. "klein" means "small" (small in scale, opposite of "big"), whereas "kurz" means "short" (small in length, opposite of "long").
The problem arises, when you talk about the size of people. In English you usually say "tall" and "short", but in German you use "klein" and "groß" for that, which literally means "small" and "big". Things are treated differently in different languages.
Kurz is specifically used for things, for example, "Der Rock ist kurz", while klein is generally used for people like in this question, but I think there are some exceptions to that as well like "Die berge sind klein" is correct while if you replace klein with kurz here, I am not sure if it'll still be accepted. Also, in general, kurz= short and klein=small. But here, it translated klein to small.