Die Geschwister sehen einen Elefanten.
DuoLingo says that only ( The siblings see an elephant. ) is correct ... isn't ( the siblings are seeing an elephant ) also correct
see: Common Phrases http://duolingo.com/#/skill/5a397ca5fb6b4430c294c3b43c6ba585
@Dieter_Drawe: Technically that would be correct, but usually verbs of immediate perception like 'to see, to hear' aren't used in progressive forms in English. British English seems to be stricter than American English in this respect. Just my two cents as a non-native speaker. EDIT: Note that in sentences like 'I am seeing my doctor' 'to see' isn't used as a verb of perception but in the meaning of 'to visit'.