Since you entered on a K1 (based on your timeline), AOS'd and received your GC, you should qualify to file in the 90 day early filing period (roughly a year after you filed the I751, consult the early filing calculator). There are a lot of opinions as to should one wait to file the N400 until the I751 is complete. My opinion, and the path my wife followed, is that if US citizenship is a goal, there is no need to wait, file the N400 when you meet all the filing requirements. As @OldUser already outlined, your children will obtain citizenship through you, you can apply for a US passport for them using your naturalization certificate
Good Luck!