I agree with Snowthy, Family Circus might be cloying to some, but it's not all that bad. In fact, there's an anthology of the first few years of the strip from the early 60's, and was quite edgy at times. I actually liked it when I was growing up back in the 70's. There might not be anything edgy or provocative, but to a younger reader there's still a certain appeal.
But given the precedent set by the three holiday specials (Christmas, Valentine's Day, and Easter) a feature film could get quite sugary (the cinematic equivalent of eating a whole jar of Marshmallow Fluff)- so watch at your own risk.
Although it might've been nice, I'm glad Bill Watterson had the integrity not to exploit Calvin and Hobbes (he's received a number of tempting offers, but turned each one down). So at least there's no regrets that his creation will ever get tampered with (only the bootleg decals of Calvin peeing on a wall, which Bill gets no residuals for).