There is no question that Aleksei was ill with a bout of hemophilia in April of 1918, and that his illness prevented the family from being transported together to Yekaterinburg. As has been discussed here and on similar threads, it's impossible to know for sure whether that hemophilia attack was brought on by Aleksei's sledding down the steps, or by a chronic cough which worsened that same night.
Further, sledding on the steps was *not* an accident; it was a deliberate playtime activity.
I've been comparing documents from the IF's imprisonment in Tobolsk and found and interesting bit of information regarding Aleskei's sledding on the steps and his last attack of hemophilia:
I'd always thought the sled ride and the final hemorrhage happened within 24 hours of each other. Massie and other sources certainly present the events that way. However, according to Aleksei's own diary, he received the toy sledge and boat on 25 March. He and Kolya spent that day playing with them on the steps. According to Alexandra's diary, Aleksei's hemorrhage began on the night of 29-30 March, a full four days later. In the meantime, Aleksei and Kolya practiced archery and broke up pools of ice in the yard. Alexandra attributes the hemorrhage to a bad cough, which she mentions for the first time on 30 March.
I'm no medical expert, but IMO this four-day delay between Aleksei sledding down the stairs and developing his last hemorrhage makes it less likely that the two events were directly linked. Particularly since he was active and apparently in good health between the two events.
