Both sentences are possible, and they do carry different meanings, Guest. ' -- in the context of the sentence (the conversation, essay or whatever) this is the first mention of these children, they are presumed by the speaker to be new to the listener. '-- here, in context, the children have already been mentioned or are presumed previously known to the listener.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.