B4's a great car, but as I found to my surprise at club when beginers buy one the front end can be a little week. I would go for following
Brass bulkhead
brass or nylon front brace (screws to the brass bulkhead with mutch better larger screws)
Maybe with a driver of 5 I would look at maybe alloy front uprights and stub axel holders etc,I don't normaly like them
,but I think you maywell need to go for strength.
The back end of the car is quite strong maybe the odd rear tower, but get a couple of sets of wing mounts,as they tend to go if the car has a hard landing on the wing. front shock shafts,shock ends seem another favorite...infact after some thought get as many bits for the front end as you can
You will want to add a bit of weight to the rear of the car to balance all the brass up at the front.
Keep it slow,what I forgot as I have been driving for years is,, we let off the throtle as things start to go wrong, thus impacts are softer and break less KIDS DON'T!
you can stand at the side of the track watching it all go wrong and they are still flat out! thus the resulting impact is nearly always a bigun
Thing I found with kids is hold as many spairs as poss, as they can break bits you would never have thought of
.