Kittens of a rather thin week.

Hello!

I kittens for a week now and I find them quite meager. I have weighed yesterday and they weigh 106, 106, 107 and 112 grams. Yet I read that kittens weigh 100 grams at birth, so I'm a little concerned.
Unfortunately I do not know whether the kittens are born prematurely because I found the mother in the street it three weeks ago and I have collected.

Could you help me and tell me if this is normal or not?

Thank you for your answers!

Do you have the mother with you? If not, how much and how often are you feeding them? What exactly are you feeding them?

If you weigh them every day you will have a lot more information about how they are doing.

Yes, I have the mother with me! 
With regard to weigh, I started yesterday and I counted again today to see how many grams they take in a day.
This is my first litter so I do not know if the mother was going to accept that I touch her kittens from the early days especially since I did that for three weeks.

They are very small for their age but this is probably because their mother was living on the streets and wasn't getting enough nourishment. Feed the mother cat as much as she wants, try to give her kitten food or mix some kitten formula into her food for extra nutrients. Goat's milk is good too. They'll be starting on solid food soon themselves, that will take some strain off the mother cat.

That's great news! How much did they gain each? Please do keep dry kitten food down for mom and feed her wet kitten food as well. As much as she can eat!

Do you plan to keep mom?

It sounds like the kittens need supplementing with either full fat goat's milk or kitten formula. They are very small for one week old. It sounds like mom is not producing enough milk. Do you need instructions as to how to feed the kittens?