This paper pursues new understandings of the ways that ‘child’ and music/soundsensing/soundmaking come to matter in the cultural institutions we recognise as Museums. We compost (Haraway, 2016) data generated from a recent qualitative pilot study which asked whether normative Museum practices offer possibilities for very young children to encounter space, place and sound in generative ways. We reported an assemblage of findings that illustrate the ordinary, yet always political, entanglements of bodies and matter (Elwick et al, 2019; Burnard et al, 2019; Osgood & Burnard, 2019). Theoretically framing our investigation by feminist new materialism and deploying Barad’s (2007) concept of ‘spacetimemattering’ creates possibilities to think differently about the nature of agency, relationality, and change without taking these distinctions to be foundational or holding them in place. This prompts a speculative reading of multi-sensory, corporeal, affective encounters with time and space, as uninterrupted flows of ‘nows’ that matter (in terms of materialdiscursive constructions). In this paper we also attend to ‘spacetimesoundmattering’ in an attempt to consider the possible implications that anthropocentric intentionality has for children's playful experimentation. What if childhood is conceptualized as a space-time-sound continuum where what we think we know about early childhood music education is opened up to new possibilities that transform how we understand the nature of children’s engagements with/in museum spaces? Can attending to the unexpected found in affective encounters and generative soundings of young children in museums offer possibilities to reimagine childhood, music and museums?