Ah, America love it or leave it -- how original.
George W. Bush didn't love this country enough, following your logic, to serve in Vietnam, unlike John Kerry, who put his life on the line for it.
I work for peace, and I take offense at the idea of working for it is childish. I do things like lobby Congress to stop research on a new generation of nuclear weapons. I talk to people in educational forums about what alternatives to war are (stronger emphasis on diplomacy, enforcing international human rights law, curbing arms sales to dictators, et al). I also lobby on spending less on the Pentagon and more on schools and healthcare. And, yes, I sometimes attend demonstrations.
I've learned the most from people like Mina's grandparents, who are in their 70's and 80's (hardly children) and share that same passion for making things better. You can love your country (and there's much I do appreciate) by wanting to help make it better.