It's absolutely possible to use HoomKid with headphones or earphones that are to be plugged into the jack plug on the side of the device. However, ensure the volume is not too loud and suits your children's age.

HoomKid's maximum loudness is limited to 85dB (decibels) in compliance with WHO's recommendations.
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​Is it compatible with all headphones? Does the dual headphone plug-in work for any headphones or just your brand?

You can connect any set of headphones you want! We recommend using a set designed for children's ears just because of comfort and sound limitations.
Our own HoomKid headphones come with a socket to plug in an extra pair, not the device itself. But you can plug a set by any brand into that socket.