I find the whole thing about the whipping incredible and I don't think it's true. I've never heard anything like that from any sources. From all I've heard, Nicholas and Alexandra hardly disciplined their children at all, other than to scold them occassionally when they were really bad.
Nicholas himself, and his siblings, were never really given discipline from their parents, who didn't believe in corporal punishment, and barely believed in discipline at all. When still a boy, Nicholas and his family would get into food fights at the dinner table and his parents, who always enjoyed childish games and pranks themselves, would often join in.
Once, when Nicholas was still a young man, he and his brother George played a prank on their father, Tsar Aleksandr III, by waiting for him to lean out his study window below as he always did, then they dumped a bucket of water on him. He later got them back by doing the same to them when he got the chance.
Scolding was the extent of their discipline, and it was the same for Nicholas and Alexandra's children--perhaps with an occassional 'sitting in the corner' or 'grounded' type of punishment. But they never hit or spanked their children. It was not part of their nature or their beliefs.