Do you mean she has been feeding them for the past 3 weeks but has suddenly
stopped?

three weeks is sometimes when they start to wean.  Make sure the kittens
have access to soft moist food.
Chances are she is allowing them to nurse, but just not when you are around.

If they aren't able to eat on their own, and she honestly isn't nursing
them, they'll loose weight very quickly.  If this is the case, you'll know
cause the kits will be screaming all the time, then you'll need to find a
supplement and feed them yourself.  I use KMR, but there is a home made
supplement called kitten glop (google will give you the recipe) that a lot
of people swear by.

You already got good advice for the kittens. I wanted to ask -- have you
checked the mom? Sometimes they get infections in their teats and it's
too painful to nurse. Check those for any abnormalities and if anything
looks unusual or red, etc. -- get her to a vet right away, even if it's
an emergency vet.

Good luck, let us know how they're doing.

Rhonda

First, get everyone to the vet ASAP. There could be many reasons why this is
happening and your vet is the best person to investigate this issue. It is
very important that you do this, your mother cat could be very ill, or she
could simply be rejecting her kittens. Only your vet can rule out illness.
Then, your vet will give you great advice about how to proceed.

One of the reasons why it is crucial you get mother and kittens to the vet
immediately is because kittens cannot go very long without sustenance...
mother's milk... and if they get too weak it will be difficult to care for
them.... they could all die. GO TO THE VET!!!