Honestly, how do you determine whether your toddler/preschooler children are learning enough?

I know that views on this vary widely and that everyone's standards are different, but I'm curious about what kinds of guidelines you use to determine if your toddlers and preschoolers are learning enough. So, what kinds of things do you expect to be baseline knowledge, still learning but has-a-fair-grasp knowledge, and will learn soon enough knowledge?