of course you can put a newborn in a cargo bike. It's no different than a car if you have the proper equipment.
How about a cargo bike at 20km/h? I can twist my foot while jumping on the ground, however I wouldn't say that base jumping is the same since you go up in the air in both cases.
So yeah, I probably wouldn't take my infant on busy roads shared with cars, but i absolutely would put on a cycle path.