Translation:The young baby weighs three kilograms.
I was going to bring up this same issue. If the Irish phrase "leanbh óg" is meant to distinguish a baby from a child (which can also be referred to as "leanbh"), then it seems like a better English translation of "leanbh óg" would be "infant" or "newborn."Translating it as "young baby" is awkward and unnatural for a native English speaker, who would almost never use that phrase except in a weirdly specific context.
It's not noticeably slender, because the distinction between broad and slender consonants is much less in Munster Irish - http://www.teanglann.ie/en/fuaim/leanbh
For example, a slender "d" is essentially a "j" in Ulster Irish, but it remains a "d" sound in Munster Irish-
Even "s", which is usually the easiest letter to distinguish between slender and broad pronunciations, sometimes retains a broad pronunciation in Munster:
(In fairness, you will sometimes find it written with "broad" consonants - "ansa" and "ansan" in Munster).