Hi Going mad,
I'm in the same predicament (although not a lone parent)... my daughter is 23 months going on 14. I've found that always having a pack of dextrose or other fast-acting glucose right to hand is an essential requirement.
It's a good idea to explain your diabetes to your son - you'll be amazed by just how much he will understand... my daughter already understands that dextrose is "daddy's medicine". Very soon she'll be wanting to help me restore my levels when I'm going low... I suspect you son will want to do the same.
If you're not a pump user, it may be worth discussing this possibility with your healthcare team as this could help to stabilise your blood glucose levels as well as give you access to a larger supply of test strips, which are being restricted in many areas of the UK at the moment in a blind-alley, short-term, cost-cutting exercise.