It should be "Could you all write some sentenceS that start with "How about....?" How about a walk in the forest? How about cake for dessert? How about we go to sleep now, it's late.

How about that? How about those Dodgers? How about fixing the drain in the kitchen today? How about we talk about this later? How about my kid? I'm no English expert (I just speak it!), but I think we usually use "how about" to mean "what do you think about____" or "how do you feel about _____." Hope that helps! :-)

how about a pizza? how about going out now?