Unhappy customer

I bought cloths at Clothing junction on lay-buy for kids, it was on 23/11/2019, Yesterday i went to take out the lay-by. when the child fits some of the cloths there were small. I ask the elder one to go and exchange the size. they were refused to exchange. I need to know what I should happen to the small size clothing because i cannot give them away. I don’t have money to buy another clothing. I need to know their return policy; do they tell the customers about their policies before the customers do lay-by please assist.