Feeding Stray cat. Trying to protect kittens, but they like to hide in car engine

So I started feeding a stray cat I saw in a backyard. I felt bad for it because it is blind in one eye. Little did I know the reason it was in my backyard was because it must have recently had kittens around the bushes, and was not going to wander too far away. Anyway, the kittens I am going to take a guess are about 2 months old. They aren't very big but I would say maybe 1/3, to 1/2 and adult cats size. How old will they be when they stop going into car engines. I unfortunately learned the hard way that kittens like to do this, because after turning on my car to let it warm up, when I came back outside I saw one of the kittens under the car with blood coming out of it's mouth. I rushed it to an emergency vet, but it could not be saved, so at least whatever little life it had left, it was humanely put down, and no longer was suffering. The other kittens however continue to go into the car engine. I always check now, but they are starting to wander to my next door neighbors house. I told him about it, but I don't think he will remember, or care to remember to check his hood every time he starts his car. How long until the kittens are big enough that they won't fit into the underside of the engine? I just have a bad feeling in my heart that sooner or later more of these kittens, through no fault of their own, other than being silly kittens, will be in the wrong place at the wrong time and face the same death. 

An adult cat can fit into an engine compartment, so it really isn't because they're kittens.  Is it cold where you are?  They may be seeking warmth under the hood.  Or it may be they need someplace safe from predators.

Are you able to provide them with shelter of some sort?  It can be as simple as an upside down Rubbermaid tote, with a doorway cut out of the side.  You can use an ordinary doghouse or you can buy feral cat shelters if you can afford it.  Put straw inside it and it will be nice a cozy.

Before you do all that, though, you need to have all the cats, mom included, fixed and given their shots.  If you are going to continue feeding them, you do not want them breeding anymore.  Depending on where you are, there should be low-cost spay/neuter groups that can help you.

Good luck and thank you for helping them!