WordNet (r) 3.0 (2006):

nursery rhyme
    n 1: a tale in rhymed verse for children

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "nursery rhyme":
   English sonnet, Horatian ode, Italian sonnet, Petrarchan sonnet,
   Pindaric ode, Sapphic ode, Shakespearean sonnet, alba, anacreontic,
   balada, ballad, ballade, bucolic, canso, chanson, clerihew, dirge,
   dithyramb, eclogue, elegy, epic, epigram, epithalamium, epode,
   epopee, epopoeia, epos, georgic, ghazel, haiku, idyll, jingle,
   limerick, lyric, madrigal, monody, narrative poem, ode, palinode,
   pastoral, pastoral elegy, pastorela, pastourelle, poem,
   prothalamium, rhyme, rondeau, rondel, roundel, roundelay, satire,
   sestina, sloka, song, sonnet, sonnet sequence, tanka, tenso,
   tenzone, threnody, triolet, troubadour poem, verse, verselet,
   versicle, villanelle, virelay