This might be an unpopular opinion, but I'd say it's more natural for kids to relate the word 'three' to 'third' and 'four' to 'fourth', instead of 'two' to 'third' and 'three' to 'fourth'.
Yes, that's why its hard to explain to kids that a two-year-old is in their third year of life. By the time of their third year of school (second grade) they usually get it, though.
We should be careful not let such easily observed facts inhibit our efforts to dumb down curriculum.
Kids are taught units, so they express themselves properly and are understood by others. e.g. The third item over here is at a distance of two cm from the left edge.
I am doing my best in teaching my kids this way but the world around has the wrong idea. We'll see how it goes...