"It's Made For Kids" is an excuse used to dismiss criticism for video games made for younger players.
It is well known that kids are easier to entertain by simple things that adults may find boring and vice versa, which is why video games targeted at younger audiences tend to be easier and simpler than games targeted at older players.
Often when games meant for younger audiences are criticized for poor quality, short length, excessive hand-holding, underestimating player intelligence, or being overly simplistic, some might use "It's made for kids" as an excuse for doing so. While it is understandable that kids may have a hard time with complex games that adults may like, saying that "it's for kids" shouldn't be an excuse for making low-quality games and excessively easy games that grown ups will be likely to dislike. This excuse also treats kids like unintelligent beings with no taste.
A good game meant for kids should be simple enough that kids can understand and play it with little trouble, yet have enough content and substance that older players will find interesting and fun to play so that when grown up gamers go back and revisit the games they played in their childhood they can still have a good time.
Even if a game is aimed at kids the adults may also be interested in it. There are many games meant for kids that can also be enjoyed by grown ups, for example the Super Mario Bros., Ratchet & Clank, and Pokémon series of games. There is NO excuse for making a bad quality game just because of who it's targeted towards.