I'm a little concerned about letting them play with dead creatures at such a young age/pre-vacinations etc but that's just me, maybe? Having brought up kittens, I've always been keen on keeping them and their environment clean.
However they sound lovely. My personal rule is to get them vetted regularly so perhaps the first thing to do is get your vet to check your chosen one/pair over thoroughly. Here's a lost of things to consider when choosing I've stolen from the web...
A healthy kitten should have:
Clear eyes with no tearing or discharge. The eyes should be fully open, focus normally, and be able to follow your finger or a piece of string dragged across the floor.
A clean nose with no nasal discharge, sneezing, or labored breathing.
Clean ears with no odor, head shaking, or scratching. Black granular discharge could indicate ear mites.
Gums that are pink, with no sores or ulcers in the mouth or on the tongue. The teeth should be white and properly aligned. There should be no odor to the breath.
An anal area that is clean, with no discoloration, matted fur, of evidence of parasites (tapeworms may look like cucumber seeds).
A clean, soft coat with no dandruff. There should be no evidence of parasites, e.g., lice or fleas (flea dirt may look like tiny black-red granules, which dissolve into red on a moistened paper towel. There should be no evidence of scratching or bald spots (ringworm). A kitten's coat will usually not appear as glossy as an adult's.
A symmetrical body shape, and one that is neither too thin nor has a protruding belly, which could indicate a severe intestinal parasite problem.
A good appetite and be fully weaned.
No lumps or bumps - including at the umbilicus (belly button).
Coordinated movement, with no head tremors. Some cats may have extra toes (polydactyly), but this usually does not cause a problem.