Not noticed a thread about it yet but I just discovered "help to save" and thought I'd share.
If you're entitled to working tax credit (I think anyone claiming for childcare gets the WTC element of CTC) then you should also be eligible for a "Help to Save" account.
You put away £50 a month (or £10 or £20) and after 2 years the government will pay a bonus of £600. After 4 years provided you continue to pay the maximum £50 a month you receive another £600 bonus. The bonuses are 50% of your highest balance over that time so even if it's £10 a month it's well worth doing.
You can apply by going into your gateway account where you would usually update your tax credits claim.