The poem 'Let's Play' by Kate Greenaway celebrates the end of school and the beginning of playtime. It speaks of lessons finished and play begun, with children eager to run fastest and laugh loudest. The poem uses various punctuation marks to convey its message and structure.

The author of the poem 'Let's Play' is Kate Greenaway.

The phrase 'Play begun' signifies the transition from the structured environment of school and lessons to the freedom and joy of playtime. It marks the moment when children are released from their studies to engage in fun, active, and unrestrained activities, as suggested by the lines about running fastest and laughing loudest.

If the poem had used only full stops, its tone would have been much flatter and less expressive. The excitement conveyed by 'Oh, what fun!' and the enthusiastic challenge of 'Who'll run fastest, You or I?' would be lost. The poem would read as a series of simple statements rather than conveying the joy, energy, and interactive spirit of children eager to play, thus significantly reducing its emotional impact and vibrancy.

The exclamation mark in 'Oh, what fun!' directly emphasizes overwhelming joy and excitement, signaling the children's delight at the prospect of playtime. While 'Play begun.' is shown with a full stop in the provided text, if it were to have an exclamation mark, it would further emphasize the immediate and enthusiastic commencement of play, highlighting the children's eagerness to switch from studies to recreation. Together, these punctuation choices (or the specific choice for 'fun') strongly convey the theme of liberation, happiness, and the energetic anticipation associated with the end of school and the start of play, underscoring the children's sheer delight in their newfound freedom.