Maybe someone who knows a little better can offer you more concrete advice, but I believe if you file and have approved a K-1 without your children, you will not be able to apply for a K-2 for them afterwards....in a year as you say. The children have to be listed on the original K-1 application and approved at that time. There is an allowance for "follow to join," I believe, but the key is that the children have to have been approved on the original I-129F application.
I may be wrong in this, and hopefully someone w/ more concrete information can give you a better explanation.
Good luck.
-P