By JODY THOMPSON Yummy mummy: Sandra Bullock plays with son Louis and a pal with a green truck at a playground in New York yesterdaySandra Bullock was playing her favourite role of mom with aplomb yesterday when she played with her adorable son Louis in New York.The 46-year-old had taken the 15- month-old toddler to the park with a pal as she took time out from filming her latest movie. The