1-3 days old
Kittens found at this age will likely have an umbilical cord and sometimes a placenta.
3-7 days old
Kittens at this age will probably still have their umbilical cord and their eyes will not be open. Kittens separated from their mother at this age have a very low chance of survival - even with the best human intervention. Finding mom gives them their best chance!
7-10 days old
By now most kittens will have lost their umbilical cords. They generally will not have their eyes open at this age.
10-14 days old
As a rule of thumb eyes are opened between 10 - 14 days however, there are exceptions where they open their eyes as earlier. They do not really get around on their own but may start to move by wiggling. They may start to put weight on their legs.
2-3 Weeks Old
Their wiggling will start to look more like walking and they will slowly be able to get around.. They are not yet running or playing.. They do not have teeth until the 3 week mark when their front teeth start to come in.
By 3-4 weeks they are usually getting around quite well but still quite clumsy. Even at this age, they will be very easy to catch unless they dive into a small space. They can be introduced to wet food but many won't be interested. At 3 weeks they get their front teeth and by 4 weeks they will have their back molars.
4-6 Weeks Old
By this age kittens are playing and washing themselves. They bounce around and attack imaginary prey. By now they should be eating wetfood. This is when they usually reach 1lb