ILR BRP as proof of children's citizenship

[Cmackenzie]

Hello,
My wife and I have just become British citizens. Our daughter was born (in the UK) last year after we received ILR and is therefore a British citizen and has already obtained her 1st passport.
After attending the ceremony, we began sending back our ILR BRPs and I cut them in half to send them back. However, I remembered reading (on these forums?) that we need to retain our BRPs as proof of our daughter's eligibility for citizenship.
I'm now unsure what to do. It seems like a poor choice to send off the only/easiest form of ILR proof that HMPO (the passport office) accepts, but I am not sure how useful a cut up BRP would be.
As we are now citizens, we wouldn't be able to apply for a replacement BRP, which in any case would now show a date well after our daughter's date of birth.
Are there any suggestions for the best way to ensure that we have proof of our ILR that would be acceptable to HMPO?
Thanks, Campbell

[vinny]

I believe it’s best to retain them as proof of child’s British citizenship.