It's the usual, anywhere near standing or stagnant water will invariably suffer from mozzies more so than areas without breeding grounds.
When the girls were small we went to Menorca several times, its probably the most family friendly of all the Balearics - which means there are kids everywhere! In fact, other than Ciutadella, there's more kids than mozzies. Not sure I'd want to go there for a "grown up" holiday.
Don't recall mozzies being a major issue, at least not in the areas we were - but then again, it was a few years ago so maybe they were and I simply don't remember
JF