A frozen Ellis Pond became a winter wonderland for children last week as temperatures fell well below freezing. According to one neighborhood parent, the ice was between six inches and a foot deep. On Friday, Dec. 11, nearly a dozen children — along with some adults and a pet or two — were skating, playing hockey, building forts, riding their bikes and simply enjoying the rare occasion to play on a frozen pond. Officials warn that playing on the ice is never without risk.