Is cannabalistic behaviour normal

Our black Labrador (Pepsi) has just had puppies - this happened
yesterday. At about 5 am there were 7 pups and then at 9 am another 2.
Then much later at about 5 pm they totalled 11. I noticed that she was
quite rough with one of the latest arrivals, but did not want to
interfere. Last night when I checked on them, I noticed that two were
missing. I checked everywhere and also in the garden for a possible
"burial" place, but could find nothing. My only logical conclusion is
that she ate the two last arrivals (which seemed a tad smaller that the
other) to make sure only the strongest survive. Is this normal or
should I be worried that she might kill more? When I checked on them
this moning there were still 9 and everyone seemed happy and content. I
believe in letting the bitch going about her business without too much
interference from my side.