Definitely put some in a pension. Get a lump in this tax year and plan to contribute out of income going forward.
If there's a chance of you being able to buy your council property, that would probably be a good thing to do, but consider that you'll then be responsible for paying the mortgage and maintenance, which will be difficult while you're on a low income.
Which brings you on to whether it is a good use of the money to retrain, so you can earn more in the future.
But isn't your existing car that's worth £7k new enough that it shouldn't be unreliable? Might it be a good investment to trade it in for something that's newer and cheap to run?
Plan to keep a lump in savings and be mindful that while you have this money (although I don't know if it includes the childcare element) it will be stopping you from receiving top up benefits that you would otherwise be entitled to on your income and obvious as a low earner with a 5 YO, you are going to have childcare/holiday club costs over the next few years to cover.
But there are 'deprivation of assets' rules, but I don't know if these apply if you use the money sensibly, ie on retraining, pension, decent car and possible house purchase or if you just give it away.
Another consideration would be, while you say your DC won't have to pay tuition fees, they might need help with university living costs, also driving lessons, or setting up their own homes, so if they don't currently have any savings, it might be worth setting up their own savings - there's probably an investment based child trust fund type product available, that should grow by the time they're 18.