It does not accept "Küçük çocuk futbol oyuncusu olmak istiyor." But this sentence is completely natural in Turkish.
That is unusual in Turkish. But you can say like this "Küçük çocuk futbolcu olmak istiyor." You can use "footballer" instead "futbol oyuncusu".
Why not küçük çocuğu? İt says "the little child".
The accusative case is used only for specific direct objects. Subjects never get the accusative case :)
Facepalm. Elementary mistake...
"Küçük çocuk bir futbolcu olmak ister."
"a"="bir" was not translated into Turkish. "bir futbolcu" ?
It could be added but might sound a little odd if you use it. I added it as an alternative.
Does sometimes verbs take accusative before istemek ? I think I have seen a couple so far