No exchange without till slip at Jet

I bought my husband's grandkids clothes at jet for Christmas a week ago...because of the mother that can't read and write I took the wrong sizes. I've been to 3 stores keep on exchanging till Ive lost the slip. I bought it at Belville jet even they can't exchange without a slip...unless it was bought on account...it's frustrating because what must I do with the clothes while they don't want to exchange? What's so difficult to only exchange? The price tags are all still on every item...is there no other way that I can just exchange it for smaller sizes? I will really appreciate the help. Thanx in advance