If they are walking and running, they are probably at least 4-6 weeks of age. This is a great time to see the vet with them for kitten shots so you can get a good idea at your visit.
Take a look in their mouth. If they are young, they will have missing/baby teeth and you can tell.
Also, kittens start to eat kitten food at 3-4 weeks of age so you can try giving them some and see if they will eat it. This might be why mom delivered them to you! She might just need some help!
Let me know if you still have questions.