you can't lose 3 stone in that time unless you are seriously guzzling now - if you are, then eating normally will mean you'll drop a lot of weight quickly and then go down to the usual 1lb a week that is the only sensible rate.
however if you only eat a bit too much and don't do enough exercise, it is simple to turn it round.
rapid weight loss means rapid expansion again.
ok, so that was eat less move more, which IS the only one that works long term. (basic science, although many people are good at ignoring that) Here are the requested tips:
if the kids leave lots, serve them less. They can always ask for more if they are still hungry. That way you get less waste and don't have the urge to finish it up as there will be nothing to bin.
don't buy sugary or fatty crap. Not there, doesn't get eaten.
eat your complex carbs to fill you up. I had porridge for breakfast today, lasts fine until lunch.
and finally, no-one else cares what you look like on holiday. (Or at any other time)