What are the benefits to send 18mth to a playground ? For example what kind of skill will he learn from attending playground that cannot learn staying at home ?

Hi do you mean playgroup? I think playgroup can develop their social skills things like sharing , following instructions, activity as a group, interacting with kids of the same age. You can definitely teach the same things like phonics or academic stuffs at home but the social part I think it is not the same. However they will tend to fall sick more easily once they go playgroup so must be prepared for that. It is also a chance for your baby to be independent and away from you for a few hours. I feel that's good and prepares them for education later on.