the difference here is that you are thinking mathematically and your child isn't. He is obvioulsy interested in the difference between 14 and 27 , which is the asme as the differenc between 27 and 14.

He needs to undertstand the subraction oprerator in terms of something else e.g. taking away from

so 14-7 is the same as taking 7 away from 14 but is diiferent from taking 14 away from 7. Use money as an example.