Theory:

O! Father and Mother, if buds are nip’d,
And blossoms blown away,
And if the tender plants are strip’d
Of their joy in the springing day,
By sorrow and cares dismay,
Explanation:
 
The fifth stanza introduces two new characters to the poem: his father and mother. In the stanza, and that which follows, the speaker can be seen trying to make his parents see why it is pointless to go to school, especially during a summer morning. According to the speaker, a school is a place where a child's individuality and independence are snatched away.
 
The speaker compares his life to those of plants whose buds have been nipped away and flowers have been blown out. He adds that he is in a situation similar to that of a young plant whose life has been snapped away during the spring season.
 
flowers-279583_1920.jpg
Buds and blossoms

Like the tender plants, the child has just begun to grow up, but he is soon left in sadness and dismay through the meaningless education system.
 
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A child is like a tender plant
 
Meanings of difficult words:
 
S.No
Words
Meanings
1
Bud A small part of a plant, that develops into a flower or leaf
2
Nip’dNipped; having removed something by pinching or squeezing sharply
3
BlossomsFlowers
4
Strip’dStripped; having deprived someone of their possession
5
Tender Young, inexperienced, or vulnerable; (of a plant) easily injured by severe weather or careless handling and therefore needing protection
6
SpringThe season after winter and before summer, in which vegetation begins to appear; (metaphorically) relating to the period of life when one is young
7
DismayA feeling of unhappiness and disappointment
Reference:
National Council of Educational Research and Training (2008). Honeydew. The School Boy-William Blake (pp. 83 - 84). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.