How to explain boycotting the Americans to children

I'm a Canadian and I was out with my niece (3 years old) and nephews (5 and 7 years old) today and they wanted to go into an unnamed US-owned big box store. I told them we weren't going to do that because we're not going there for a little while (we're boycotting anything American to the best of our ability until the tariff challenges are resolved). I couldn't find a nice way to explain to them where they understood why we weren't going into places their parents usually go with them.

I'd be interested to hear how other people are explaining to their kids or nieces and nephews what a boycott is and why we're doing it.