Referring to adult-age sons and daughters as children

Is it normal to refer to adult-age sons and daughters of someone as children?

A native speaker of Arabic learning English has said that in Arabic, the word for sons and daughters is "أولاد" (awlaad) (Wiktionary link), and that it applies no matter how old they are, and that the word for people who are not adults is "أطفال" (atfaal) (Arabic language Wiktionary link). The person wanted to know whether you can still use "children" to mean "sons and daughters", even after you can no longer describe someone as a child in the "not yet adults" sense.

As AndrewGrimm notes, "children" has two very distinct meanings: It can refer to people who are not yet adults, or it can refer to people who are the offspring of a specified person or people.

It is normal and common to refer to adults as "children" when expressing the relationship. Saying that so-and-so are the "children of" someone is another way of saying the "sons and/or daughters of". For example, "Alice and Bob are the children of Carl." "Children of current employees are given preference in hiring." Etc. Depending on the context, you may or may not specify that they are adults. You would not say "Alice and Bob are children" without giving an "of" someone if they are adults.

Side note: "Children" (without a relationship) can mean anyone who is not an adult, but it is unusual to use it to refer to people who are more than 12 or so unless you are including them in a group that includes such younger people. That is, it would be odd to refer to a group of 17-year-olds as "children". It is more common to call them "teenagers" or "young people". But if you were talking about a group of people ranging in age from 6 to 18, you might refer to them collectively as "children". Like, you might say "the children in our school district". But few would say "the children in our high school".

It feels a bit strange, but yes.

http://education.yahoo.com/reference/dictionary/entry/child is listed as having a few meanings, but 1 and 4 are the most relevant ones here.

"1" says that it is used for people who are not yet teenagers. "4" says that it is also used for the sons or daughters of someone.

Meaning 4 says "A son or daughter; an offspring," and you may think that "offspring" is a unambiguous alternative to "child". But "offspring" is often used to refer to the offspring of an animal, so it may be slightly impolite to use it for people. It does get used, but often in a slightly derogatory manner.