"Three Russian boys are looking for a cute cat."
Translation:Kolme venäläistä poikaa etsii söpöä kissaa.
To be more precise, Finnish uses partitive singular after numerals that are in singular form. Numerals can also have plural forms. The plural of "kolme" would be "kolmet". That would trigger nominative plural for the noun, and a plural form for the verb. But the numeral is singular, which makes the noun singular, which makes the verb singular.