Absolutely yes, cats can easily squeeze into the engine bay from beneath the car. I have faced similar issues in the past when the mother cat leaves her kitten inside the engine bay and she rests underneath.
What i used to do was first shake the car gently and give some strokes on the car bonnet which will force the kitten to come down, Once after doing this process i started the vehicle and traveled roughly 2kms when i started hearing sound of a kitten crying.
Immediately stopped and parked the car, came out and repeated the above step to see a kitten coming down. After seeing this i opened the hood slowly just to ensure that no more kittens are hiding and then started the vehicle. Yes it could have easily turned out to be a messy affair had if the kitten got stuck between the timing belt/radiator fan.
But the story doesn't end here. After some time i returned back to home and the mother cat came running as it was crying in search of its dear one and to my surprise it went inside the engine bay and came out in disbelief and was crying even more louder looking at me. I was really disappointed but little i could do
after seeing this. Anyways may be because of this bitter experience the same mother cat gave birth to many more kittens after this incident but she has not attempted to climb the engine bay anymore. But whenever i see kittens around i ensure that all the above mentioned checks are done.