You have done well to recognise the different way that nature is viewed in the two different books of poetry that Blake wrote to complement each other and also to challenge our thinking about the relationship between the various states of innocence and experience. Generally, The Songs of Innocence portray nature in a way that we might call Romantic given the way that Blake deliberately associates nature in these poems with happiness, childhood memories and confidence in the future. In The Songs of Experience, by contrast, nature is given a much more sinister feel and is seen in some ways as the opponent of man and the descriptions that Blake gives us make the world seem a much more dangerous place. Let us look at the two versions of "The Nurse's Song" to explore this further.
In the Innocence section of this collection, nature is described as a haven for the innocent children, and they are described in a way that portrays them as being yet another example of God's creation being left to play in perfect peace and tranquility with other forms of nature:
Besides, in the sky the little birds fly,
And the hills are all covered with sheep.
The children are described as having an intimate relationship with nature and they obviously feel a companionship with the "little birds" and "sheep." In the Experience poem, however, we are given a completely different image of nature. The coming of night is something that is seen as dangerous and something that exposes the vulnerability of the children:
Your spring and your day are wasted in play,
And your winter and night in disguise.
In this poem, the children do not get to respond to the Nurse, and her world-weary voice attaches very negative feelings to the seasons, giving spring a sense of waste and winter a sense of danger and cynicism through her reference to it being a time of "disguise."