Ah, is your little one learning to walk? Look at it, waddling along on the brink of falling on its face any minute. That's nice.
So here we are; its rush hour, you're trying to get to the next platform to carry on your miserable commute. You go through gates, through the tunnels and do what you can to avoid Smowhawks when you're suddenly slowed to a crawl by a parent and their tiny child ambling up the stairs and blocking everyone behind them.
It's simply wonderful, heartwarming and life-affirming to see a parent and their small child having this learning experience together, but in the case of a very busy staircase, pick the damn kid up and get your ass up the stairs. No one care, no one has time. If you want them to practice stairs, do it at home.