Parents with young children not already acquainted with the Children's Museum of Manhattan, 212 West 83rd Street should give it a try. There's a variety of programming for various ages, and it's pure pleasure to see the ways in which youngsters can enjoy themselves. I went to sample a program of the Jazz-Ma-Tazz series aimed to acquaint children with jazz. The series has just ended, but here's hoping funding enables the program to have a reprise and continue as a regular feature. Hayes Greenfield, congenial and talented leader of the three-musician combo, had the room jumping. One irrepressible four-year-old with a great sense of timing and show biz rhythm joined Greenfield at the mike and was a show himself. The jazz concert was followed by another activity--painting to jazz accompaniment on the theory that the music will free and enhance the creative spirit. The children were given material on which they painted whatever they wished and when they were finished the end product was a scarf, returned to them after dry cleaning to preserve the painting. The tab for participation was $3.50. Some of the results were exceptional. Much more is part of the daily routine. For further information about programming at the museum, phone 212-721-1234.