Visible crew/equipment: After Bobby tells Alice that he can't pass Jan the potato chips because he's "not here", when Greg walks in and Bobby tells Alice that Greg's "not here either" we can see the tape mark on the floor behind Jan.
Continuity mistake: While the kids are practising the potato sack race as Jan watches from the sidelines, when Marcia steps into her sack and hops away there's a large color image on the front of the sack, but when she reaches Peter, then turns and heads back the image has vanished - it's not on either side, then it reappears when she's back with Bobby. Additionally, when Cindy hops in the sack that Greg was in, the sack is ripped at the bottom and Cindy's feet are on the grass, but when Cindy reaches Peter the bottom of her sack is perfectly intact.
Answer: Much trivia has been written about "The Brady Bunch, " including the various interrelationships and dynamics among the members of the cast. For example, much has been written about why Robert Reed's Mike Brady did not appear in a couple of episodes, including the series finale, due to rancorous creative and artistic differences with series creator, Sherwood Schwartz. However, in contrast, I have never run across any reasons given why a particular child did not appear in specific episodes - only that the episodes were missed. This suggests the causes were likely unexceptional, such as illness, injuries, vacations, or real-life family obligations.
Michael Albert
Although those options ARE possible reasons, it just seems a bit ironic that this happened all in Season 2 ONLY and within a short amount of nearly consecutive episodes. Never happened during the other 5 years of the show at all.