Sorry... I don't speak Chinese but, running it through Google Translate, I'm guessing that the Chinese is equivalent to "Careful, watch your step" or "Careful, watch where you step". However, that's more something we'd say to a young adult or an adult. I don't think we'd say that to a two year old. I'd be more likely to say "Careful, watch where you're going.".

they usually say "慢点儿" in such cases

watch out.