Following is a response from Senior DHS staff member, Tom Pullum:
The Stata lines pasted below will do this merge. In the KR file, you have to drop children with b16=. (they have died) or b16=0 (they are not in the household).
* Merge the KR and PR files, Kenya 2022 survey
* Specify workspace
cd e:\DHS\DHS_data\scratch
* Prepare KR file
use "...KEKR8BFL.DTA", clear
gen cluster=v001
gen hh=v002
* b16 is na if the child has died and 0 if the child is not in the hh
drop if b16==. | b16==0
gen line=b16
sort cluster hh line
save KR8BKRtemp.dta, replace
* Prepare PR file and merge
use "...KEPR8BFL.DTA", clear
gen cluster=hv001
gen hh=hv002
gen line=hvidx
sort cluster hh line
merge 1:1 cluster hh line using KR8BKRtemp.dta
tab _merge
keep if _merge==3
drop _merge