dukester, well done you - i think you should go for it.
Based on what does your HV say your little boy is autistic? is she qualified to make that diagnosis? i thought it would be down to a peadiatritian, but im not sure.
I did a biochemistry degree as a mature student and whilst it was tough with DD1 (i had a very supportive family who looked after her all the time for me) and be prepared for being up working til two in the morning etc, it was the best thing i ever did. I loved it and hated it in equal measure at the time, but i was interested enough to drive me on.
What i am trying to say is this, if you really want to do it, then you will fit in around your son. Of course he will come first and if your uni is anything like mine they will be really understanding. They will happily extend deadlines etc if you are finding it hard, they get enough requests from that from students who havent done a certain peice of work becaue they have been on the piss all weekend But they will make allowances for your situation. You will be allocated a personal tutor who will be a good person to make a friend of as they will back you up if you need more time etc. Generally speaking, lectures aren't compulsory so as long as you catch up (often downloadable now anyway) later you'll be fine. To be honest, most of your effective study will be self directed too, becaus the lectures just give the bare bones. You will probably have practicals to do, which are compulsary but you should know their dates in advance, and again, if you have family commitments as long as you keep the uni informed they will accomodate.
Only you know if you are up for the work load, but give it a go, you may well surprise yourself.