Beautiful music emanates from a little patch of mulch in Dorchester’s Uphams Corner, a symphony of percussive tones produced by multicolored xylophones, chimes, drums, and vibes. In perfect harmony with all that? Giggling. Lots of it. Because the musicians — the ones swinging, pounding, and tapping orange-tipped black mallets — are 6- to 12-year-olds. We’re in the playground out back of the Ray and Joan Kroc Corps Community Center, a sparkling multipurpose Salvation Army facility that opened last year in a neighborhood that badly needed it. The children, most of whom live or attend school nearby, are in the Kids Feast program, an afterschool initiative that provides athletic, academic, and spiritual activities. And all for free. During outdoor time, the instruments, arranged like shrubs around a garden, are a big hit. After all, what’s more fun than fully sanctioned noise-making? As the commuter rail runs in the background, the children improvise their own melodies — they are wonderfully consonant, reverberating through the playground in moments of spontaneous magic. When the sounds reach their ears, the players’ faces fill with delight: Did you hear that!