so the diagram is not to scale and there's some time here to react. why not just pick up the baby? run up, grab the kid, and lunge back towards the sidewalk. sure, the truck and car are going to collide atop your legs, but you'll save the kid and be able to sue ford, tesla, and both drivers. given a split second to decide, i think that's clearly the way to go.
The other lane looks pretty clear, continuing to run across the street is probably safer. I'd do the two arm waving over the head "STOP!" motion while also yelling that and looking really concerned. I'm not gonna get hit by a truck myself to save a baby. My life is worth more to me than a baby's cause it's mine. Hopefully this would cause the truck to swerve and hit the self driving car. More realistically that baby is dead, I'm scarred for life, also will be deeply disturbed that someone left an infant in the middle of a crosswalk and as a witness, help the horribly irresponsible parents sue tesla and the big truck guy/big truck manufacturer