Revealing mistake: At the beginning, as the flying saucer lands at the stadium, the shadow the ship cast doesn't change size as it gets lower to the ground.
Revealing mistake: When Tony is stacking the wine barrels in Gannon's lab, you can see the wires pulling the last barrel up into the pyramid.
Answer: In "Escape To Witch Mountain", Tony tells the lady in charge of the children's home that their foster parents adopted them when Tia was 3 and Tony was 5. "Escape" possibly takes place 6 years after they were adopted, making them 9 and 11 in "Escape", and 12 and 14 in "Return".