My 5 month old male kitten has decided to be a surrogate mom to his mom's 2 week old kittens?

he lays in their little area with them and washes them just like mom does, washing their tummies to help with digestion and washing their butts. they act like they are nursing but of course they're not. mamma cat doesn't have a problem with it. is it a problem? oh, and sometimes he nurses on mamma, too.
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