We are staying in Cannes for a few days this summer. Is the drive to Monaco worth it? Are there things to see there other than the Casino (we'll have minors with us).

We were there a few years ago and my answer would be YES! We went to the aquarium there which, in my opinion, had more interesting sea creatures than I have seen anywhere in the world. We also enjoyed walking around and visiting the Palace and the cathedral where Princess Grace's crypt is located.
I believe there is also a museum with oceanic artifacts including the first submarine, etc.

Monaco is beautiful - definitely worth the short drive.

Other than the casino (which requires that you dress, by the way - and minors are not allowed through the front door), there's shopping, museums, and a fabulous lunch in the restaurant at the top of the Hotel de Paris (minors welcome). The views are worth the price of the meal.

Monte Carlo has it's own feel/ambiance. It's really a beautiful city with gorgeous architecture and winding streets. A fun place to just stroll around. Enjoy!

Yes definitely especially if you have a few days. There's not all that much to see in Cannes so you'll want to drive around.

Yes, definitely, if you have a lot of money. IMO Monte Carlo is worth perhaps half a day, no more; too much glitz.

That's what our travel agent said Carrom, so we have reserved an auto. It is difficult to tell whether there is anything there other than the casino, which we can't enter.

Admittedly there's not much but it's the feel of the place as malbino said. I think (but you'd better check as it was a long time ago) that there's a wonderful museum of antique mechanical toys in Monte Carlo. That would be worth taking the kids to ...and the botanical garden maybe.