An only child = selfishness?

As it's widely known, a popular stereotype about only children makes us think they are generally all selfish. This ascertainment tends to be true and to be justified by several reasons. First of all, they say, only children feel the bee's knees from the beginning of their childhood, as they are accustomed to achieve what they are eager for (e.g. sweets, toys, money) without an obligation of sharing it with anyone, in contrast to those children who have siblings. Secondly, only children are surrounded by their parents' love and attention, so again, they don't have to think about anyone and to bother themselves with siblings' problems. Another reason to affirm that this stereotype is true, reffears to long periods of time only children are accustomed to spend alone, e.g. at home, when their parents are at work. Even if only children have got friends, it is a significantly different case if they had siblings, simply because we can't choose relatives, but friends.
 I could agree with a statement that stereotypes are based on some true observations and tendencies, but, as a matter of fact, probably all stereotypes are exaggerated or ignore some significant real facts about a discussed subject of any stereotype.
So, firstly, much depends on childrens' upbringing and values and priorities being taught by their parents. If parents pay attention and explain to their child (most effectively by their own example) that, for instance, everything should be shared with others or it would be a nice gesture at least to offer something to somebody, a child starts to behave so, and later it comes natural to share what he/she has got with others.
What is more, there are many cases, when children who have got siblings, are selfish and stingy thoughout their life. Secondly, it can be true, that only children love to be in the spotlight and to be surrounded by somebody's attention (but not necessarily), nevertheless, everything depends on a personality of such children and on their character. I have met many only children who pleasantly astonished me with their sincere caring about others and dedicating their time helping to resolve others' problems.
 Lastly, it is somewhat true when it comes to preferring to spend time in isolation, since only children are accustomed to act on their own, not depending on somebody's plans, and I would add that comparing to children who have elder sinlings, only children become earlier more self-relient and take care about themselves with much ease.
In conclusion, there are some aspects, that make us think only children are generally selfish, but we shouldn't forget, that a stereotype, like a first impression, is frequently misleading.