The children attracted attention onto themselves  by  shouting loudly.    

 in the sentence given, isnt onto a preposition as well of place?

or is it an adverb......

if its an adverb so why is it so 

Dear Student,

Here 'onto' should have been written as 'on to'. We will soon get the mistake corrected. 

Here, 'on to' is used as such: 'on' (adverb) is followed by 'to' (preposition) which then, stands for 'toward'. So, here it means that the children attracted attention towards themselves. Thank you.