Instead of sweet cereals, I switched to plain cereals and then add packets of sugar. Yes, it costs more for sugar packets than a bag of sugar, but I would end up rounding over a spoonful.
Anyway, each sugar packet is 2.5 g. At 3 packets, on a bad day when I'm eating my frustration, that's way plenty. And that's only 7.5 g of sugar. The sweet cereals have at least 20 extra g of sugar. Yikes!