Childhood is the best time of a person's life.
I do agree the idea that the most joyful time for every person without any doubt would be their childhood. Since people are different in many areas, they may have different opinions about the reasons; however, I believe that childhood is the happiest time because first children at that age do not have any special responsibility, and second they are children and their mind and the way they think completely different from teenagers and adults. In other words, their minds are free.
First, as a child you do not have to take any noticeable responsibility. You just play and enjoy your daily life. A child does not get into the troubles of for example studying, going to work or even having family duties like a father or mother. In case of everyday life, matures are dealing with a lot of chores and duties. Take the case of a mother for instance, she should have to take care of the house, do the daily chores such as cooking, ironing, cleaning and boring duties like that. Moreover, she has to look after of her child or children too. Considering that she does not have to work like her spouse outside the house. Children's most important concern would be the size of their bicycle or the number of their toys they possess.
Second, as a child your mind is largely free from many things which may cause challenge such as political or financial issues. Furthermore, in that period they tend to make friends much easier unlike teenagers. The things they are looking in a friendship are not materialistic. The purpose of make a link with their peers would not be for using them in further critical situations. They simply make friends to play with each other or to share their toys. Beside mentioned points, their needs are not much complicated. They would become easily happy by giving them a notebook and bunch of color pencils as if they are given a luxury car or a high-ranked position in a company.
In conclusion, I consider the childhood time as the most memorable and happiest for everyone mostly because at that age, our expectations from life and other people around us are very simple and would not cause anyone trouble.