Yikes - I wouldn't leave kids inside the house alone even with a monitor. I am always scared there could be a fire or carbon monoxide and then you wouldn't even know and it would be hard to explain why you left kids inside the house alone if God forbid something did happen.

Nothing can replace good old ears and eyes inside the house on alert even from a distance.

For the activities....I would love that sort of time with a 3 and 4 year old to do kindergarten readiness type activities. I think that would be the perfect time for them to work on gluing, cutting, handwriting readiness and name printing, colour sorting, patterns, etc one on one with you. I have a group with some under 2s and some who are off to JK this September and I have a hard time getting good learning time with my preschoolers because the little ones always want to join in and I have to sort of entertain two different groups. Having time to do kindergarten/school readiniess stuff alone with them would be perfect. Upper/lower case ABCs...more complex crafts....etc are all good ways to keep the older ones busy too.