A boat with 30 people aboard capsized on Saturday at Fisherman’s Wharf in San Francisco, trapping several passengers under the vessel’s hull before rescue swimmers managed to pull everyone from the water, though two children were critically injured, fire officials said. What caused the boat to overturn at Pier 45 along the city’s famed bayside northern waterfront was under investigation, but there was no immediate evidence of foul play, said city fire department Lieutenant Jonathan Baxter.