Why was the moron cycling so close to your car anyway
Charming.
The cyclist does not need to be very near to a car to be in danger of being whacked by a car door. They open very wide. Everyone is assuming it was passing on the left - as the car was stationary it was almost certainly passing on the right - ie the offside, and nobody should be opening a door on that side anyway.
If for any reason they were passing on the left, it does not really change anything, as you should be careful of pedestrians when you open your doors, too.
I'm not sure why people are getting so abusive towards the OP though - a child can make a mistake - and a child can be well over the age of needing child safety locks and still make a mistake.
In fact some months ago a lady pulled up next to me in the railway station car park. One of her adult passengers opened the door straight into my car. I gave them a hard stare, but I don't think they even realised they'd done it. My car isn't very new, I'm not precious about the odd scratch but it shows adults can be as negligent as children. Yet everyone gets on their high horse when a child does it.
It does not sound as if the cyclist was hurt badly which is very fortunate. Let the insurance deal with it, learn a lesson, and move on.