Ooh, lovely kitties @acsny . Nice big, upright ears, and very pretty broken tabby pattern like StefanZ has said already. Your youngster has some lovely spotting on the back too, and clear stripes on those lovely long muscular back legs - a little cat that likes to run and jump perhaps?
They're actually not related,millie we got from my cousin and she is growing like a weed and Brutus we adopted from a shelter! He is very playful and very cuddly. I've always thought millie was perhaps a Maine coon because of the tufts of fur in her ears