I think that you can put it into perspective for kids to realize that they are really blessed. It is very unfortunate that some people have to live on the streets and it is really difficult to explain that not everyone's situation is the same. Helping the kids realize that they have more is one way to put it.
it'd be pretty hard to explain poverty to children. but what you can say is that some people aren't given equal opportunities to find work and earn money. what not to do is to tell kids that poor people are poor because they're lazy.