Thanks for your question.
A certificate of entitlement or partiality in a passport showing the holder has the right of abode in the United Kingdom or a stamp in a passport showing the holder is exempt from immigration control is not evidence that he or she is settled in the United Kingdom. But some persons who have certificates of entitlement or partiality or who are exempt from immigration control can nevertheless be regarded as settled in the UK.
From the information you have provided above, if you have not transferred your stamp into subsequent passports, I would be of the opinion that the permission has lapsed.
Thus, in order for you to obtain UK Citizenship, you need to look at other avenues.
From the information you have provided above, it would seem that at least one of yoru parents was a UK National.
If this is the case, you should be eligible to apply for UK Citizenship. Click on the following link for further details:
Once you have registered as a UK National, your child should be able to obtain a UK Ancestry Visa.
If you wish to discuss, please feel free to ask further questions.