Hi, your friend is right to be concerned about her son and his condition.Sepsis(blood poisoning) can be extremely nasty, and is typically caused by bacterial infection which effectively overloads the bodies own defence mechanism. (It can less commonly be caused by viruses and fungi)
In the instance you describe, the age, the breathing difficulties etc are all of concern......but on the positive side, he is now in hospital, his condition has been recognised, and he is receiving treatment. The blood tests will be to confirm the nature of the infectious organism.
They will have immediately placed him (I would imagine) on IV antibiotic therapy, and possibly O2 therapy as well, to fight the infection and to aid with his breathing.
So, its potentially very dangerous... but your friends son is in the best place, and having the right treatment. Your friend will obviously be extremely worried, but they should try to be as positive and optimistic as they can.