I disagree with PPs; I think it's worth having a plan. Firstly, it's extremely unlikely you'd both be desperately ill, never mind at the same time. But, in theory, it could happen.
You say you've no support, but in a situation like this, you need to draft in anyone who can help - is there a school class WhatsApp group, for instance? Do you have neighbours? If you go onto a local Facebook group or the Next Door app, you can connect with some of your neighbours. I know our local group has people offering help if it's needed - you could offer to help others if you're well, and then maybe you'd find it easier to ask for help?
I'd concentrate on making sure you had someone coming once a day with food. Even if you just leave them a key, they open the door, set it in the hallway, and go. Sandwiches or something would be fine for the kids for a couple of days. Get disposable cups or something that they could put milk into for the toddler.
If you were both really ill and unable to even get out of bed, social services would have to step in and put the kids into short term foster care.