Insulin is a substance that protects, coats, and insulates neurons, helping connect impulses from one neuron to another.
I believe there were researches on the toddlers' behavior, and I guess the main purpose of any curriculum for infants and toddlers is based on their needs. I think it mostly relies on the kids' preferences and needs because the curriculum would be ineffective otherwise. For example, if my daughter wants to have a playground, it will be useless for me to buy her a book. I'd try to carefully implement the educational process in her games, so she will still be entertained and not feel pressed.