Most MG novels are in the 20,000 to 40,000 range. However, there is a wide range. I researched publishers for my MG books and a few were looking for books as short as 15,000 words and a few others were looking for over 40,000 words.
I think 25,000 words will be fine for your novel as long as you are able to tell your story well within that length and not rush any parts of it.
I also read somewhere that for first books, publishers are more willing to accept shorter pieces than longer pieces because they are eaiser to sell.