Now i am hoping someone can give me a logical reason for what i have just seen, i would love to be proven wrong as it will play on my mind if i'm not.
Now i have no children so this may be one of the cases where as i am not in the situation so i don't know better IYSWIM.
So.......i have just seen a woman on a bike with a child on the back in a cycle seat. With a baby attatched to the outside of her in a sling! 
Now to me that seems extremely unsafe. It is pouring with rain, in a busy city centre with idiot drivers. Rush hour. Is it me that thinks that the sling could come undone, the baby is soaking wet, and if she slips or falls off the bike, she could easily land on the child and hurt it or something even more terrible?
Please tell me if i am being unreasonable or can someone explain to me how this is actually safe?