Note about the "girls" ... they fledge later than their brothers, can be up to 10 days though I don't think that will be the case with Isis (red) though Aura (green) could just take her time. If they don't fledge for the next couple of days, no worries, that is very normal. They are bigger and it takes longer for them to develop enough to handle flight - remember females are usually half again the size of the males. Isis will probably be that when she fledges, not sure if Aura will be, so far, she looks a wee bit smaller than her sister, but definitely larger than her brothers!!
And for those of you worried when they fly ... keep in mind that the peregrine chicks have been doing this for a few thousand years now so they pretty much have the kinks worked out evolutionarily speaking. Yes, the nest on cliffs, that gets them up above all the stuff they have to worry about flying into. The nestbox is high, but it is actually the safest nestsite we have for fledging chicks in the city - despite the other tall buildings. For those of you in Winnipeg, think about where the building is situated, except for the Kensington Building across the street, all the buildings for a block in all directions are lower than the Radisson nestbox. And the Kensington Building isn't a big concern because its on the east side of the Hotel and the box is on the west. So chicks jump off and aim for a high building a couple of blocks away, they immediately lose a bit of altitude, then start flapping and with enough distance, they gain altitude again and that's how they stay up above it all. We have a FledgeWatch in part because we can, in part because we want to increase the chicks chances for survival in their first year and lastly because until they figure out how to gain altitude when flying, they have a greater risk of ending up down on the ground and they don't yet have the strength or skill for the vertical take-offs that we are so used to seeing with the adults. They make it look effortless, but it isn't, takes a bit of time to get all the various mechanics coordinated.
First couple of days are the highest risk in terms of getting grounded. Once they have been out and flying for a few days, being able to get back to the nestledge is usually a good indication that they are quickly mastering the necessary skills and the risk of getting grounded goes down significantly.
The chances of getting hurt are ever present but getting hurt due to inexperience decreases daily - then its just hurt due to an accident rather than first flights and their is nothing one can do about that really. In Ohio this year we have had two deaths in the last week and a bit - a fledgling on I believe his/her first/second flight, that would be a fledging death in my records and the death of the resident female which is one of those tragic accidents that happen to peregrines - no reason, just an accident.
And as a final note, we have far fewer fledging injuries/fatalities from the nestbox than the nestledge, so altitude does have its advantages.