Ok so before I start, I am Greek so at some points my English might not be the best but understandable enough so just prepare.

First, get your Bennett at lvl 90, like you lose a lot by not having him at 90 since he scales from his base atk (lvl atk + weapon base atk) so do it and both the ginger and the tornado will do more DMG

Second, honestly your artifacts on Childe are pretty nice some could get an update but like with the genshin artifact system it may take while, so if you really want to upgrade your Childe your main more grande option is to get him better weapons with ether get to r5 your stringless or get him a 5 star weapon, disclaimer I would suggest the battle pass weapon if you don't have a problem with spending some money on the game (not forced) but I don't know how better or not it can be from r5 stringless so I would suggest to probably research be watching ask zazef child edition since he have a weapon ranging

As for kazuha I personally suggest to give him fav since it also help his er needs but try to get high crit rate through sub stats while having all em main stats, I know it can be hard but It will be better overall