More than anything else, kids need love and attention from adults
The young brain can absorb a surprising amount of information. It is incumbent on the parent to curate a learning environment which constantly develops new neural pathways.
At ages 3-8, the primary developmental goals are linguistic and social. Success criteria: be able to conduct oneself appropriately in varied social settings, ideally in multiple languages.
To attain the above:
No TV, ipads, or video games. These stimulations are engineered to be more appealing than pretty much everything the natural world can provide. Removing access to these stimuli allow the brain to calibrate around tasks that require delayed gratification and long-term focus
Exercise and fresh air are a daily necessity, and ideally integrated into normal life, rather than "boxes to check"
Allow stuff to break. Creative thinking is possible when children can explore their surroundings. If parents chide them too frequently for doing the wrong thing, this inhibits willingness to explore. So unless it's a safety issue, or forming bad habits, I give my son a lot of leeway to touch/sniff/lick/yell at whatever is in the house
Systematically build opportunities to practice and benefit from delayed gratification.