When they are building the house of cards, Marcia's first card is a two of spades. In the next shot it is a six of spades.
Jan's hair keeps changing from straight (when the shots show the house being constructed) to pulled back (in the close ups of the girls)
When Marcia is trying to place a card on the tenth level of the house of cards, the shots cut between her holding her arm to stop the dangling of her bracelet to her not holding her arm (depending on the direction of the shot).
Early in the House of Cards game, during Jan's turn, her card changes from an Ace of Spades to a Five of Clubs, then back to the Ace of Spades.
After the house of cards is knocked down, two of the cards remain standing up.
At the end of the House of Cards game, after the cards fall, three cards remain standing as they are glued together. Robert Reed/Mike Brady even tries to flatten them out, but they spring back up.
During the building of the house of cards, you can see a television up against the wall, in the background, they already had one.
At the trading stamp redemption store, the clerk shows the girls two sewing machines, and even though he describes different features, both models are exactly the same.
Between the 6 children, & both parents looking through the stamp redemption catalog thoroughly, it is doubtful they wouldn't have seen that there was a color television available, for the number of books they had saved. One can't imagine children choosing a rowboat, or a sewing machine, over a new color television.