"Two small children are admiring a large tree."
Translation:Kaksi pientä lasta ihailee suurta puuta.
Because the subject is modified by a singular numeral, which triggers partitive singular, and the verb must agree with the subject about number, i.e. whether it's singular or plural. The plural form of the numeral would be "kahdet", meaning "two pairs", which would trigger nominative plural instead and cause a plural verb.