am travelling short- and long-haul in c-class, both alone on business and privately with family (including now 7 and 5 year old daughters) - not on miles or ID tickets
even when our kids were not the quietest for short periods of time, fellow travellers did show hindsight, conceding that they are children.
all in all we have been faring well - bar that gentleman who had to continue from SIN to MEL with a pair of soiled slacks (air-sickness) after he gracefully assisted me when our little one was ill - but even he took it with style and accepted by spare pair of jeans (two sizes too big, but the belt did it)
when travelling alone in C-class, it has usually not been the behaviour (or lack thereof) of small children, but more often the behaviour of fellow adult passengers in various states of intoxication or making uncalled-for and offensive comments to cabin-crew (mainly female...) in regards to appearance, indecent proposals, a non-available choice of meal, 'restrictions' on quantities of liquor served, delays, bumpy flights, mal-functioning in-flight entertainment systems - you name it.
edited for syntax....