Earplugs

"Alpine Pluggies Small Sized ear plugs are made especially to fit young children comfortably, from about age 3 up to adults with small ear canals. Pluggies feature thermo reactive hypo-allergenic silicone for a comfortable and effective seal in the ear. Pluggies also have an acoustic filter that lets the user clearly hear all that is going on around them, but with just enough attenuation to take the sharp edge off noises in the environment (SNR 19). This feature makes Pluggies ideal for those with hyper sensitivity to noise and can greatly enhance concentration in school or while studying at home for almost all children."

http://www.earplugstore.com/alpine-pluggies-swimming-earplugs.html