Hi Vance, congratulations on getting your kittens this far and them being healthy…no small feat!
You can start now by introducing them to wet food. There are several ways you can do it. Mixing with formula/milk and opening up nipple so food and milk can flow through or mixing the same gruel and putting it on a plate and letting them sniff and lick, or putting wet food on finger and letting them sniff and lick and put a dab on the roof of their mouth letting them taste it. You can usually tell right away which ones are interested, which ones are not. The uninterested ones, the bottle with the food works best. It gives them more nutrition and gets them used to the taste and their bodies processing something different than just plain milk.
This is also the time when you can introduce the litterbox to them. Make sure the box is easy to get in and out of and use plain, unscented, non clumping litter. Kittens think everything is food and will sometimes eat litter, so non clumping is best for now.
Bottle Babies