This is level 1 of the A-Tunnel.
In this level, there are lots of crumbling tiles, which are made into different paths. If you have the Child, then he is obviously the most preferred character in this level, because he can run on the crumbling tiles without letting them crumble, which is very useful. You just need to jump high and reach for the next platform, then repeat the process. In this way, you can beat this level with ease.
As for the Runner and the Lizard, just do high jumps to jump between platforms. Don't panic when the tile you are standing are about to crumble! You can still run and jump on them.