Environmental component

Hi.  My husband haas ADHD that was diagnosed at age 33.  We now have two kids, ages 4 and 2.  I have read on this site that there is a strong environmental component, but I don't really know what that means specifically.  What I'm wondering, are there things I can do in our household that would help my children at this stage?  Neither has a diagnosis and I don't have any particular concerns.  If there's anything I can do to help them, (not get ADHD?  present more mildly? cope with it if they ever are diagnosed?) I want to do it. 

I would also be interested in hearing what I should be watching for in my children.  In so many things, the earlier people are diagnosed the better, so I don't want them to go until age 33 before they find out they have ADHD.