The idea that every gadget, or even most should be child-safe is silly. Alexa is an internet connect device at the end of the day and should be treated as such by parents. However, where possible companies should also try to avoid situations where they're causing unnecessary harm and if needed government should step in to regulate to protect consumers.
In this case, it seems right that people are flagging this up and are unhappy, but I do tend to agree with the sentiment that kids probably shouldn't be using Alexa anyway and that the risk here isn't really comparable to car safety where regulation absolutely makes sense.
On a personal note I honestly hate how often health and safety regulation gets in the way of what would be cool products and experiences these days, but this is the natural result of people refusing to take personal responsibility. It's likely this feature (which I'm guessing doesn't do this in 99.9% of cases) will now just be removed because it can't be implemented with 100% safety.