Interesting that in just a few short decades it has become perfectly 'normal' to send toddlers off to school.
The first 5 years are the single most important stage in a child's development. I get that everyone needs babysitting. No-one seems to want their young children around the house all day. The role of Mothers has changed so much that she wants and needs more time away from demanding young children (and boy are they demanding!)
Over here in Asia 'pre-school' and 'nursery' means scheduled instruction time. Group reading at 10am, paint play at 2pm etc.
If you have the time, energy and money and are purely focused on the brain development of the young child, then a stimulating home environment offering plenty of resources for curious minds is the best avenue you can take. If you can afford it then hiring a babysitter/aupair type (someone who will actually do things with the child and not just watch TV) is a great addition.
Children do not actively group-play until they are around 4-7 years old. Prior to that they 'parallel play'. This means they play alongside other children but do not actively seek much engagement in order to develop the understanding of the task at hand.
But I do get it, and especially among the Thai Mums, they seem to love the structure, lifestyle, uniforms and 'cuteness' of their little toddlers going off to school everyday.
Just don't be in a rush to start the institutionalised learning if you really could adapt home and all the loved ones there to nurture the young mind(s) at home and around your local community. ????