Blue Tit Babies In Downpipe

Hello can anyone give me advice on what to do about a nest in a pipe please? It’s a thick cast iron down pipe that is unused and the nest seems to be 2-3 feet down it. Four little chicks look quite well grown and feathered and are being fed by the parents. 
I’m concerned that while the parents can somehow manage to get up and down the inside of this pipe, the little ones won’t be able to scale it. 

should I try to move them? Or maybe put a twig in the pipe to help them climb out?