If you go into Options, then General Settings. In there uncheck the one that says Enable Shop Mode. That will stop them from showing up in game.
I'm not fond of the idea, I mean they already added the shop mode where you can buy things in game. Adding them to the catalogue seems to be just trying to earn even more revenue.
I agree too that someone and not necessarily a child could easily buy something by mistake.
**edit** OK, to buy something, first you have to select it from the catalog, then click the button that says how many simpoints and then you need to confirm your purchase, so buying by mistake might not be as easy as I thought, although if you have young children who play, it might be wise to have it turned off in the settings as they may not realize what they are doing.
Norma