If the cat is scratching its ears and you can see black grit, that's
probably earmites. Consult your vet for appropriate ear drops. Ear mites
stay in the ears, but can be passed from cat to cat, especially if they
groom each other. The life cycle of an ear mite is entirely within the ear,
so you do not have to worry about ridding your house of them the way you do
fleas. Cats typically shake their heads when given the medication; unless
the medication actually comes back out, that is OK. An additional step to
take is to soak a cotton ball or pad in mineral oil (baby oil is fine), and
clean out the outer ear (do not poke into the canal). That rids the upper
ear of any ear mites lodged higher up than the canal, and makes it difficult
for the ear mites to reestablish themselves.
Scratching and a discharge from the ears means a bacterial or fungal
infection and the vet should be immediately consulted. Other possible causes
of scratching include fleas, lice, eczema, allergies, or stud tail (in male
cats

Ear mites are common but I'm not sure you can do much. But just wait
until you have to put the drops in your kittens ears. Fun!

One dose of Revolution will take of it!