Music is not an add-on to early childhood. Rhythm, song and musical play are foundational to language, motor development and social bonding.
The human brain is wired for music from before birth. Foetuses respond to rhythm and melody in the third trimester. Infants prefer infant-directed speech, the singsong, exaggerated rhythm of talking to babies, over normal adult speech. Nursery rhymes, songs, and rhythmic movement are not cultural ornaments on childhood; they are among its most powerful developmental tools.
Research by Sandra Trehub at the University of Toronto has shown that musical engagement in infancy, particularly parent-sung songs, improves attention, memory, social bonding, and language acquisition. The rhythmic structure of music overlaps directly with the rhythmic structure of language, meaning that musical play is simultaneously language development.
Key citation
Trehub, S.E. (2003). The developmental origins of musicality. Nature Neuroscience · Trainor, L.J. & Corrigall, K.A. (2010). Music acquisition and effects of musical experience. Springer Handbook of Auditory Research
Britain's oldest toy maker. Every toy open-ended, wooden, and built for exactly the kind of play the research recommends.