Try sending your toddler to "school" where they are required to sit still and learn on a fixed schedule. If you've got very young children, you know how unlikely that is to happen: playing is the way toddlers interact with the world. That doesn't mean that you have to be content with giving your child whatever toys happen to be around and hoping that they learn the necessary developmental skills. There are certain types of toys that can help speed them along in their learning, especially with cognitive and sensory development.
By age two, toddlers should be well on their way to mastering a few specific thinking and motor skills. Learning by trial and error is an important one, as is matching items (putting a round peg in a round hole), and being able to identify familiar objects. The beauty of educational toys for toddlers is that they're designed so that you can give them to your kid and these skills will arise naturally from play.
Take ring counters for example. These toys help build both color identification, sorting, and counting skills in children. As your toddler plays with the toy, the identification of the similar rings is what comes first, by putting rings of the same color on the same spoke. As the child realizes that each color has their own spoke, the number of rings on that spoke will become associated with the written number on the bottom of the toy. All three skills of identifying, sorting, and counting are interlinked, and the simpler ones help build more complicated ones.
Sort and stackers are essentially simpler versions of ring counters; they're great options for younger toddlers, less than 18 months old. While the skill of counting is less emphasized with a sort and stacker, trial and error learning is more important; toddlers learn the order in which the rings go on the spoke, as well as the logic of size.
And, while cognitive development is important in toddlers, so is fine motor skills development, like learning how to move things with their hands and fingers. As they get used to manipulating the rings and stacking components of the toys, they'll get the muscle memory they need to do other important tasks, like move a spoon to their mouth and wash their hands.
Giving your child toys that are especially attuned to their developmental stage is a smart move, and the toys don't have to be complicated and expensive to have positive results. While they won't start preparing your toddler for the SAT, they will help them meet important developmental milestones and satisfy their innate curiosity and desire to learn.