Translation:We play with the farmer on the farm.
Typical Dubs, thinking it's all fun and games on the farm. Bet they never skulled a weanling. ;-)
In both cases, the nouns are eclipsed because of the preposition is combined with the definite article. "With a farmer" is "Le feirmeoir" but "With the farmer" is "leis an BHfeirmeoir." "On a farm" is "ar fheirm" but "on the farm" is "Ar an BHfeirm."
Note that lenition rather than eclipsis could be used for this sentence in Ulster Irish.