Our child renewals took about 7 weeks recently – arrived the day before we were due to travel so we had a last minute panic to rebook everything/get packed (the whole thing was pretty stressful!)
We did online applications and the advice at the time was 3-4 weeks. The thing with that advice is that it’s always retrospective so it doesn’t take into account surges in demand (by the time it mattered the advice had changed to 5-6 weeks).
My wife’s renewal took 3 weeks, but that was dealt with by a different passport office. Liverpool/Bootle and Peterborough seem to be particularly slow.
We also figured out that there seems to be little “process” in place – turnaround times are completely random and luck of the draw… the helpline is infuriating too as (with one or two exceptions) they are completely unhelpful or just say whatever they need to in order to get you off the line (and that’s if you don’t get cut off when on hold).
On the upside, TNT were very quick and efficient – so they saved the day in our case.
In the future, if we need to renew less than 10 weeks before travelling then we’ll be going fast track!