nzshar - don't worry, I'm probably too laid back too! I'm very much of the "Anything for an Easy Life" Brigade (within reason, of course). However, that doesn't mean that the children run riot, eat what they like and trash the house (well, actually, yes - they do trash the house ...)
Parents send their children's meals as I don't want to have to supply them myself. I am fully-booked with every age range, and really don't have time for cooking (and don't want my non-working hours used for child-related work). In the ideal world, parents send relatively healthy food, but not always. I endeavour to supply healthy snacks, but the schoolchildren sometimes have chocolate HobNobs!!
I don't see a problem in exploring cupboards so long as you don't mind them pulling out what's in them, and so long as it isn't bleach! My mindees love to take all the base cushions off the settees, tip all the toy boxes out, put the buggy blankets over the top, and chuck a few used kitchen rolls and cereal boxes in for good measure - parents arrive and think we've had a tornado.
I don't think you can be ultra-strict with other people's children - you need to keep a check on inappropriate behaviour, and you may need to be a bit assertive occasionally (or post on mumsnet for advice!), but you need to have a sense of humour, lots of patience, and you need to have fun.