This song teaches the children subtraction. Every time a snowman melts, but it is actually mentioned by that 'shhh' which is meant to bring attention to the fact that they were 5 and some of them melted. one by one.
I sang it with my children this winter several times and in the end, I asked them why do we say 'shhh' and we half-rise our fingers? and the answer came straight away 'Because they are melted'.