(1) Actually I'm pretty sure the reason there are so few dead kids is 1. The alpha kids have no time player and 2. Dave was very careful about not creating doomed timelines whereas Aradia (and possibly Damara) actually made a point of creating as many doomed timelines as possible--so she could have her army of doomed Aradiabots.

The alpha kids’ session and the beta kids’ session were always meant to merge together. Dave is their Time player. The eight player session was foreshadowed here.