While the quote speaks directly to kids, it's true of all believers.
As kids learn about God's goodness and holiness, they ought increase in awe of him. That's growth. And as they examine themselves and the ugliness inside, they ought to increase in conviction of sin. That's growth too. But the combination of these will drive them to despair - unless their understanding of the forgiveness and righteousness they have in Jesus also grows. (pg. 54)
Quote taken from Show Them Jesus by Jack Klumpenhower ©2014 by New Growth Press.
When we focus on God's goodness and the reality of sin only; we are at best focusing just on law, and at worst just giving them a half gospel. We need to focus on the whole gospel, the forgiveness and righteousness we have in Jesus as well. We need to focus on the entire gospel ... often, more often than we do. We do this for nonbelievers as well as believers (who arguably need it more in order for continued growth).