Do I think it is a good idea for my children to learn another language? Emphatically, yes. I, along with almost every other parent I know, do not wish to see my child crushed in whatever future global competitive job market that is coming. An acquaintance of mine has a child that is tri-lingual, speaking English, Arabic, and Spanish. This, of course, makes me feel anxiety that my kids are going to be left in the multi-cultural dust.
Of course you can buy them just for simple exposure to another language (and by extension, another culture), but if you are truly looking to teach your child another language, don’t fool yourself that these will do the trick.
You might be better off getting some flashcards, but I would recommend a) having someone fluent in the language speak to your child on a regular basis or failing that, b) classes. If your child is a bit older, something like this will probably do the trick, as second language courses in public elementary/middle schools have already gone the way of the dodo due to budget cuts, if they were ever there to begin with.
Let’s face it, your child is not going to become fluent in Spanish just because she presses a few buttons once or twice a day that sing “rojo” and “verde.” Trust me on this one.