He is a big name in Psychology circles on the cognitive development of the child. From the Wikipedia article: "Piaget was second only to B. F. Skinner as the most cited psychologist of that era."
https://www.experimentingwithbabies.com/experiments/
which covers a lot of simple experiments (that should be harmless), the theory behind them and what result you can expect to see. Children develop quite fast, so you've already missed the first half of the book! But book 1 covers up to 2 years, and you can look at the sequel for beyond.
It includes things like the spot/mirror test, seeing what toys kids are interested in based on what adults look at, etc.
(I feel I should point out I don't have kids, but I would definitely want to try this out if I did. As far as I can tell none of these experiments should cause any ethical concerns, but you should be the judge of that since your child can't give consent!)
Of course main subject is criticism of school but it also has a lot on learning and how child brains work (and how they don’t)
I have a 14 month old son, and am really interested in just generally understanding the cognitive development of kids and how they learn about the world over time.
Are there any good books on the subject?