sustainability and growth

we're reading an article for inquiry class about sustainability and the major theme is that population growth is the major fault for issues of sustainability.  i agree in some senses, because as the population grows you do need more resources for them (or they use more resources).  i've always thought of myself as a fairly sustainable person.  i walk places, i recycle, i turn off the lights and keep the heat low (much to my roomies' chagrin) but reading about this has made me think.  i've always wanted a big family, lots of kids to fill the house and to feed, but the article is making me re-think that.  i still want a family, don't get me wrong, but what about setting an example for the rest of the world by self limiting ourselves to 2 kids.  is that so bad?  obviously we can't make any laws determining the number of kids you can have.  but my thought is that if you want more than 2 kids (and can support more than 2) why not adopt to fill your family.  i know that takes extra money, and i wish that it wasn't so complicated and expensive a process, but that's what i'm thinking i want to do.