Tom and his parents often-------(go) to bed at half past ten

often这个词表示汤姆和他父母所做的是经常性的动作.这种情况下,尤其是后面没有指过去的状语的情况下（如last year去年）,用一般现在时就行了,即动词原形go.这是语法的第一步.所以,整句就写成：Tom and his parents often go to bed at half past ten.
汤姆和他父母经常十点半睡觉.