This bike trailer of my sister was with all that. My 3 year old niece managed to rip apart a cover and stuck her hands outside. The bike rode near some poles, causing potential hurt. My 4 year old nephew in the same trailer was close in "trying out what happened if I stick my finger there" (the wheel). I had to make a yell to impress him enough to stop. Luckily, I was cycling behind.

Likewise, if your kid gets acute illness (throwing up, dizzy, etc), you're not going to notice it right away.

I would go as far as outright banning these things for transport of living beings, with hefty fines for it. Please stop selling these things for living being transport, you will make the world a better place and have better margins on cargobikes.