Although children (tu brakuje slowa np AND) later adults who grew up without (przedimek) sibling have rather different memories and sometimes characters than people with siblings. Nowadays more and more people 'decided' (teraz. - decide) to have only one child because firstly they want to find a well-paid job. (a co to ma wspolnego z jednym dzieckiem - napisz)
There can certainly be some real advantages of being aN 'one' ONLY child. At first one child has usually more toys, clothes 'and the other things' (np jakie - musisz napisac - nie uwazaj ze czytajacy ma sie domyslac) . Parents buy him a lot (brakuje slowa) things. They spend more money 'for' (zle slowo, tutaj ON) their child and 'it' (chociaz nie lubie jak mowimy o ludziach jako 'it') whatever it wants.
This child 'musnt`t' (napisaklas calkowicie cos innego co mialas na mysli - tutaj chcialas napisac DOES NOT HAVE TO) share a room with anybody.
ON the other hand upbringing of (tu brakuje slowa) only child has some 'dark sides' (napisz disadvantages). For example they 'hasn`t' HAVEN'T anyone to play with them and they are usually bored with playing alone. On 'the' (niepotr) top of that they sometimes can`t (tutaj brakuje cos - moze learn to)share with 'the' (niepotr) other people because they have everything for themselves.
So all in all being an onLY child in (przedimek) family is probably a good thing, BUT IT also has bad sides.