Though my dog River is huge and fierce looking, children are fond of him because he doesnt have a(n) _______ disposition.

barren?
interrogate?
humdrum?
sullen?
trickle?
truce?
vicious?

I would think that vicious would be the best word to fit the blank. It makes sense, because children would be scared of a dog if it was vicious. If the dog was friendly(In this case it is), lots of children would love to be around that dog. I hope this helps! :)