When Roger Button goes to the store to buy clothes for his son, he is distressed to find that there are no suitable outfits for a 70-year-old man. The problem, of course, is that he’s looking in the boy’s department. What we see from the start is that Roger’s insistent self-delusion is the big problem here. If he accepted the fact of his son’s age, gave in, and went to an appropriate store, he wouldn’t have a "shameful secret" to hide from the store clerk (1.2.7).
Instead, Mr. Button ends up purchasing a rather ridiculous fancy dress-suit consisting of "dotted socks, pink pants, and a belted blouse with a wide white collar." As the narrator says, "The effect [on Benjamin is] not good" (1.2.27).
We see Mr. Button’s denial again and again in the first few segments of the story; he insists that Benjamin play with a rattle, break things around the house, and play with children his own "age." In his attempt to keep his son as normal as possible, Roger ends up making the situation all the more bizarre.