A Year
After the first season, it really is clear that the Brady children look a lot older. The reason for that is because a full year passed between the pilot episode and the beginning of season two.
Workforce
All throughout the series run Florence Henderson kept pestering the producers to allow Carol Brady to get out into the workforce. Henderson believed this would be far more in line with how she was in real life. However the producers kept Carol Brady unemployed, although she frequently participated in volunteer work and fundraising for charity.