I suppose it depends on what you are planning doing, when we went last year, we were aiming for the ultimate relaxation/chilling holiday, we were staying in a villa with a private pool, so during the day we were based at the villa with the occasional trip out around the island. We ate lunch at the villa except when we were out . Some evenings we had a barbie, other evenings we ate out in local restaurants. We took about half of what you suggest, but did put meals out and some of the supermarket shopping on the friendly plastic. We didn't skimp on anything we wanted, bought snorkels, lilos etc and bought booze home and we still came home with quite a lot of Euros. It also depends on the age of your children, as they will be wanting ice creams etc, my two are older (16 and 12 at the time) and were not really bothered about being entertained and doing things and were quite happy just to use the pool and snorkel in the sea. I believe that Menorca has hiked it's prices up quite a lot in recent years. Are you taking just Euros or are you able to have a flexible friend as back up? Also check out the Menorca Forum if you haven't already, I found it so useful to have lots of info about places to go and places to avoid before we went..
http://www.menorca-net.co.uk/menorca/menorca-info.php