Thanks Larry, I will attempt to copy & paste my original question to give you a background.
Original question:Category: Child Benefits
>I turned 66 in Dec. 2017, I have an 18 year old child graduating high school
>in June 2018. I have not yet enrolled to take any benefits. I would like to
>retroactively take my benefits and child benefits and then suspend, letting
>my benefit compound until I am 70. Considering my child graduates in June,
>when and how should I file and for how many months will we be paid. Thanks

Hi,

It won't do you any good to file for and suspend your benefits if your intent
is for your child to receive benefits on your record. Due to the 2015 Social
Security amendments passed into law by Congress, your child couldn't be paid
child's benefits while your benefits are suspended
(https://www.ssa.gov/planners/retire/claiming.html?intcmp=AE-RET-PLRT-REL...).

You could claim benefits retroactively to December 2017 for both you and your
child and then suspend your benefits after he or she graduates, but in that
case you won't receive delayed retirement credits for the months that you
receive benefit payments. Still, you may feel that receiving 7 months of
benefits for both you and your child is an acceptable trade off for
sacrificing roughly 4.66% in your eventual benefit rate. If your child isn't
disabled and is age 18 and graduates from high school in June 2018, then June
would be the last month for which he or she could be paid. You may want to
consider using our maximization software to run your numbers and see which
strategy you consider to be best in your situation.

If you do decide to apply, you'll need to file your applications no later
than the end of June 2018 in order to be able to claim retroactive benefits
effective with December 2017. You may be able to file online at ssa.gov, but
if not you can file either by phone or in person at a Social Security office.
You can make an appointment to file by calling 1-800-772-1213.

Also, if you do file and then want to suspend your benefits effective with
July 2018 you'll need to tell Social Security no later than June 2018.

Best, Jerry

My current question is:
But I thought filing retroactively in June would take me back to an effective date of January. Would I not have to file in May to collect for December?

Hi,

You can potentially claim up to 6 months of retroactive benefits not including the month that you file your application, but you couldn't go back any farther than the month you attained FRA. So, if you attained FRA in December 2017 you could file anytime between now and June 30 2018 and still have the option of choosing December 2017 as your month of entitlement. If you filed in June, the 6 months of retroactive benefits would be December 2017 through May 2018.

Best, Jerry