I too have been wittering on for years to all who will listen. The special credits do not take anything from the (usually) mother. If the parent of the child(ren) who is claiming child benefit and works in a job that pays at least the starting point for National Insurance, which I believe is £184 a week, then a credit can usually be made for that year to the carer. I claimed for 4 years until my state pension kicked in. I stumbled across this credit by accident. Had I not, I would have had 4 empty years on my record.
Also, anyone retiring from 2016 who receives or will receives a private pension, having “contracted out” years ago, will find their state pension reduced. When the pension scheme changed in 2016 lots of women, myself included, have found they are short of the full amount. These credits can boost your state pension.
As with the changes to pension age that hit women born in the fifties, these special credits aren't widely publicised. Also, paying gaps from way back may not increase your qualifying years. Its always best to phone DWP and ask them. Don t leave it too late!