The adult ISA and Lifetime ISA allowances have been kept unchanged.
Up to £20,000 a year can be invested in a standard ISA each year.
Laura Suter, personal finance analyst at AJ Bell said: “Parents will see a massive jump in the amount they can put away in a Junior ISA each year from next month, with the limit more than doubling from the current £4,368 to £9,000.
“It’s the biggest jump in the allowance since the Junior ISA launched in 2011, but with the average subscription per account being less than £1,000 it’s unlikely to be a boost many households will use.”
Rachael Griffin, tax and Financial Planning expert at Quilter, said: “In a budget which was very much focused on the here and now of responding to the Coronavirus, it is pleasing that Sunak has committed to providing a helpful boost for a new generation of savers by more than doubling the annual subscription limit for Junior ISAs and Child Trust Funds to £9,000.
“Although this will be music to the ears of many Junior ISA holders who may be currently hitting their subscription limits, it may not be properly considered by many Child Trust Fund holders. Since they were scrapped in 2012, many parents will have forgotten that they even opened up an account and will not be aware of this generous increase in the subscription limit.”
Adrian Lowcock, head of personal investing at investment platform Willis Owen, an investment platform in the UK, said: “This is a truly eye-catching change, doubling what can be saved in a JISA or CTF, and allows parents to save truly life-changing amounts for their children tax free. It also acts as a way to encourage savings for the next generation, helping to ingrain a vital long-term savings habit in our children.”