You may file I-130 for your child (F2B) after you get the green card. Then, the I-130 can use the priority date (PD) of your I-140 as the I-130 PD.
See this link (read "Retention of Priority Date" part):
http://www.hooyou.com/ageout/childemp.htm
See this link (read "Retention of Priority Date" part):
http://www.hooyou.com/ageout/childemp.htm
