K.W.
If kids are breathing, they are learning. It's inherent to being human. The question is "what are they learning?" The next question is "what do you want them to be learning?"
If you start doing large amounts of rote learning children are very young, for the most part what they learn is to memorize, recite, comply with schedules, and do what they are told. They are learning to perform on cue. For some parents, the ability to perform on cue is highly valued. It certainly leads to high test scores, especially in the younger grades.
If you do the more unstructured, whole child approach, they learn different things. They learn to think critically. They learn to make good judgments. They learn to connect information in novel ways. They learn how to live comfortably in their own skin, how to move smoothly and with control. They learn how to explore a complex subject and learn about it. They learn to be confident in themselves as learners. They learn to take responsibility for their own education, and study things independently.
The second approach tends to to lead to children who are less compliant and less capable of performing as expected on cue in the younger years. If you give them an instruction, they are more likely to ask "why?" than immediately comply. Their expertise may be in areas that are not tested on standarized tests, and thus have lower test scores. However, they are more likely to excel in advanced topics in high school and college.
To summarize, here's the basic sequence
Early-cram method:
1. learn to perform
2. learn to comprehend
3. learn to integrate knowledge from many sources
4. learn how to learn, become a self-educator
Unschooling approach:
1. learn how to learn, become a self-educator
2. learn to comprehend
3. learn to integrate knowledge from many sources
4. learn to perform
I will note that there are a very few areas where early exposure does make a genuine difference. There is a learning window for foreign languages. Earlier exposure is helpful, and most people who truly master a language learn it as children. Riding a bike is a lot easier as a kid. Learning to swim is a lot easier as a kid. Learning to move comfortably in your body is a lot easier as a kid. If there is any area of actual disorder, it is usually easier to fix it in younger children.
But in most areas, it doesn't make that big a difference. People have become very talented readers, mathematicians, musicians, athletes, etc, despite starting as older children, teens, or even as adults. The kids who start at age three may look more impressive at age 7, simply because they've had four years of practice. This doesn't mean the advantage will still be evident when they're 18.
This is not to say that flashcards and such are bad. We have them around the house. My four year old loves playing with them, as a toy. She's learning a lot. Unschooling doesn't mean you forbid flashcards, it just means you don't require them.
Explore your own values, know your kid, and make the decisions that are right for you.