The principle of needing 750k to get 30k a year is talking about buying an annuity. (When you buy a product that promises to give you 30k each year for as long as you live in return for your 750k.) There will be winners and losers taking an annuity depending on if you live a long or short time. I wouldn't buy an annuity with this money as I would be too worried about living only a small number of years and losing 600k plus that I could leave to my family (if I instead chose income drawdown).
We started pensions for our kids. (Stock market trackers with Virgin Money). We started with £20 a month for our eldest who is now 10. We chose the option to increase contributions by 10% each year and now he is 10 we are paying £47 but we could put this back down if we ever needed to.
We have started a pension recently for the youngest (nearly 2) straight in at £50 a month.
I see this as the most important thing we can do for our kids due to the compound interest benefits of starting early.
If you have a frugal lifestyle and can't afford to save anything then I am sorry and I hope that your circumstances improve.
We don't have sky or any subscription tv etc (saving maybe £30 a month compared to people that do)
We have second hand mobiles and pay as you go sim (saving maybe £20 each over new phone contracts so £40 between us).
We both drive 10 year old Kia Picantos costing about £2.60 each in monthly road tax (saving £15 each month in tax compared to a bigger/more guzzly car so £30 between us in tax alone as well as savings on cosy of newer car and cheaper repairs than many brands)
There are little things too like having a chippy tea sometimes but cooking our own fish to save a tenner on the cost.
We have no savings of our own and some debt but do pay into our work pensions.
If you can't save anything but do have pay for tv, a contract phone or expensive car or spend a lot on leisure and eating out it might be worth you thinking about how you prioritise your spending.
I will go without a lot of luxury to save for my kids but obviously I won't go without any necessities and would stop payments if they affected basic groceries, heating, basic clothing or even the kids participation in school and out of school activities.