Well... since 9/10s of parenting is demonstrating an appropriate role model, the simplest way is to be grateful. Thank them for what they do, appreciate it when they are careful, thoughtful, generous, or anything else you expect and take for granted when it appears, or criticize when it's absent. Children who are not appreciated are unlikely to experience the value of gratitude themselves, and highly unlikely to demonstrate it toward others.
Remember that saying 'I want that' is not the same as asking for stuff. There are lots of things to want, and our media is awash in cool looking stuff... Just saying 'I want' doesn't necessarily mean 'I expect to get' or even 'I genuinely desire that' -- just, well, an immature expression of appreciation: I like the look of that.
"There sure is a lot of stuff to want," is a fine answer to the constant requests... Of course it has to be coupled with not actually giving them everything they notice in passing...
at 11:59 AM on Jun. 19, 2008