Two US cases allege the firm lacks consent to create voiceprints that could let it keep track of a youngster's use of Alexa-enabled devices and thus build up a "vast level of detail about the child's life".
Amazon has said it only stores data once a device-owner has given it permission to do so.
And it says parents can delete a child's profile and recordings.
Lawyers involved in the cases are seeking damages for the two plaintiffs involved, as well as others who are being invited to join the class-action lawsuits in nine states where it's claimed Amazon is in breach of privacy laws.
Amazon said in January more than 100 million devices featuring Alexa had been sold worldwide, ranging from its own Echo speakers to third-party products including headphones, fridges and televisions.
"Amazon has a longstanding commitment to preserving the trust of our customers and their families, and we have strict measures and protocols in place to protect their security and privacy," a spokeswoman told the BBC.