It is 100% NOT your fault, if they are autistic, their brain will have started developing that way before they were born, and it was probably genetically determined from the moment of conception.
My eldest (6) is diagnosed autistic and my youngest (3) is on the pathway to diagnosis, and honestly it's not nearly as terrifying as I thought it would be 3/4 years ago, when our journey started. Things I've learnt along the way
Embrace it - don't try to minimise or make them into NT kids if they're not, they may well be wonderfully different kid, and that fine, hard work but fine. Go down the rabbit hole of special interests with them, discuss and try to understand how different sights, sounds, textures etc make you and them feel, go to autistic/ neurodiverse groups and stare down anyone who raises an eyebrow at stemming, ear defenders or chew toys.
Build a team of people - it's great you have your childminders support, you will probably spend the next year talking to health visitor, school/nursery senco, pediatrician, speech therapist and more. Try to get them all on board, they're all working to help your DS in different ways, the more people pulling together the better support you can get.
You will spend a lot of time doing paperwork. I was filling in forms for the best part of 2 years - development observations, EHCP, DLA, start your research early as it gets pretty intense if it all comes at once.
Change the environment not the child - this one isn't always possible or appropriate but when it is possible, go with it. Eg. If noise upset them get ear defenders or keep things quiet insted of trying to make them get use to it. If mainstream schools to busy, push for a placement that works, if partys or outings are to much, don't go. Once we cut out all the changeable stress factors, DS then had capacity to deal with the things we couldn't change.