After navigating the flood, you come to a low wall where you can climb out of the water.
Start running forward and jump onto the slab of debris with white paint.
Run to the end, jump, and grab the bent sign. Press Interact at the prompt to hang on. Then pull up on top of the sign.
Turn left, scurry to the end of the sign, then jump onto the crane.
Run up the crane arm...
...and jump to grab the streetlamp, which swings around to the right, so you can jump onto the red-tiled roof.
Slide down the roof onto another flat piece of wreckage.
Run forward, jump to grab another streetlamp, swing forward, and jump onto a metal container that happens to be floating past.
Before it can move too far downstream, run to the end and jump to grab the low wall ahead.
Pull up and run up the slope. Jump at the end and press Interact to latch onto the rough wall with your climbing axes.
Climb up and around to the left as the building erupts in flames around you and the bottom of the wall crumbles away.
When you can't climb any farther to the left, jump toward the painted scaffolding and scramble up to grab onto the top.
Pull up, turn right, and walk toward the light blue wall. Scramble up it to grab a handhold above.
Then start climbing to the right. Jump past a gap in the ledge to grab on the other side. As you continue around the corner, the wooden moulding sinks alarmingly but holds so you can keep going.
Continue climbing/jumping to the right.
No matter how fast you go, there's nothing you can do to help the little boy. :'( So suck it up and jump past the big hole in the brickwork. Then scramble up the wall to grab a handhold above.
Climb onto the roof to end the level.