Marketing around children can be tricky business for fast-food restaurants. With convenience and price as their biggest draws, these shops are popular with busy parents. But people are especially sensitive when it comes to kids' nutrition. There's a fine line between a popular snack and a parental target.

Yum! Brands' (NYSE:YUM) KFC restaurants stepped right up to that line this week. The company revamped its kids meals, introducing a new line of them called "Li'l Buckets," which are small versions of its popular family-size meals. Yes, KFC made the kids meals healthier than they were before. But we're still talking about buckets of food.

Source: KFC.

The new meals start at a light 200 calories for the healthiest version, complete with a grilled piece of chicken and side of green beans. Of course, the calorie counts ramp up if you choose the fried chicken option with, say, the mac 'n' cheese side.

KFC said that its kids meal sales had dipped after it started offering them in adult-styled packaging. So it was high time for a change. According to the company, it has brand strength around the concept of eating from a bucket, and it wanted to apply some of that "bucket equity" to the kids meals.

But even with no help from kids meals, KFC has been beating out McDonald's (NYSE:MCD) lately. Same-store sales rose by 4% at KFC last quarter, trouncing the 0.3% boost that McDonald's managed. The fast-food king gets a lot of business out of its Happy Meals, and so this could be a new push by KFC to ramp up competition there.

McDonald's is no stranger to controversy around the nutritional value of its meals. That's one reason that the company counts "promoting children's well-being" as a key brand message for 2013.

The main risk for KFC is in blowback from parents who don't like the idea of their kids eating buckets of anything -- even if it is relatively nutritious. Sure enough, critics took to Twitter to complain about the new meals right after the announcement. A KFC spokesman told The Wall Street Journal that they amounted to a "fairly vocal, but a small group."

If that's as bad as it gets, KFC might have succeeded in this balancing act. And the prize is a new tool that it can use to pry sales away from McDonald's -- by the bucketful.