How important is the playschool for children?

Just quite important.

I answered your question before, and I still don't know what you mean by "playschool". When children are 3 and 4 in the US, they can go to pre-school. They do both educational and fun things, and they are better prepared for going to school. Many studies show that children who go to pre-school do better when they start elementary school. 

critical to their development, imho.  kids NEED to be socialized into playing well with others, as well as developing or discovering abilities and knowledges for use in later school and growth. Although unsolicited, I recommend Montessori schools unless your child absolutely hates them [and not just school in general].  Montessori methods do not work well with every child, and they do [at least in early years] for what our experience is the majority.  Disclosure:  I have no direct or indirect interest in any Montessori school, nor any family employed in one. Experience is from knowing children who attended one and if/how well it set them up for later in life success. -- Grampa