Namby Pamby is a term for affected, weak, and maudlin speech/verse. It originates from Namby Pamby (1725) by Henry Carey.
Carey wrote his poem as a satire of Ambrose Philips and published it in his Poems on Several Occasions. Its first publication was Namby Pamby: or, a panegyrick on the new versification address'd to A----- P----, where the A-- P-- implicated Ambrose Philips. Philips had written a series of odes in a new prosody of seven-syllable lines and dedicated it to "all ages and characters, from Walpole sterrer of the realm, to miss Pulteney in the nursery." This 3.5' line became a matter of consternation for more conservative poets, and a matter of mirth for Carey. Carey adopts Philips's choppy line-form for his parody and latches onto the dedication to nurseries to create an apparent nursery rhyme that is, in fact, a grand bit of nonsense and satire mixed.
Philips was a figure who had become politically active and was a darling of the Whig party. He was also a target of the Tory satirists. Alexander Pope had criticized Philips repeatedly (in The Guardian and in his Peri Bathos, among other places), and praising or condemning Philips was a political as much as poetic matter in the 1720s, with the nickname also employed by John Gay and Jonathan Swift.
Carey's Namby Pamby had enormous success. It became so successful that people began to call Philips himself "Namby Pamby" (as, for example, in The Dunciad in 1727), as he had been renamed by the poem, and Carey was referred to as "Namby Pamby Carey". The poem sold well and has been used as children's literature since Carey's day.