Many parents don’t realise they can turbo-charge their children’s tax-efficient savings in the year they turn 18.

The standard ISA allowance is currently £20,000 a year, but 18-year olds can also benefit from the full Junior ISA allowance of £9,000 in the same tax year. This creates a one-off opportunity for parents, or grandparents, to shelter £29,000.

To maximise both, the Junior ISA needs to be funded before the child turns 18, with the regular ISA taken out between the child’s 18th birthday and the end of that tax year.

Money saved can be invested in either shares or cash or both, but from April next year, the maximum cash limit on a regular ISA will be £12,000 for those aged under 65.

Parents should remember that once a child turns 18, that young adult has full control over their savings plan. While many may use funds to pay university fees or save for a future house deposit, others may choose to spend it differently.

While this allows parents to build future savings for their children, HMRC is attempting to reunite young adults with an estimated 750,000 unclaimed Child Trust Funds(CTFs), by writing to thousands of 21-year olds. CTFs predate Junior ISAs and were opened for children born between 2002 and 2011, with the government contributing £250. It’s estimated there is £1.6bn sitting in these ‘lost’ accounts, with an average balance of £2,200.