Why a pensions might be better than a Junior ISA for your kids

Ed pays £50 a month into a junior ISA for each of his sons. At 18 it's legally theirs, and he can't do a thing about it. So what happens if he uses a pension instead?Full descriptionEvery month he puts £50 into a junior ISA for each of his two sons. On their eighteenth birthdays that money becomes theirs outright — no conditions, no drip-feed, no veto.So Ed modelled the alternative: the same £50 a month into a junior SIPP, a self-invested personal pension. Children get 20% tax relief despite paying no tax, which means £50 goes in as £62.50. Over a lifetime, that relief alone is worth £82,000.The catch is that they can't touch it until 57 at the earliest, and probably 60 by the time his sons get there.Chris and Ed work through the whole model — the tax relief, the charges, the inflation problem — and argue about whether an 18-year-old can be trusted with the money at all. We both end up somewhere we didn't expect.The numbers, at 8% growth and 0.5% annual charges:£10,200 paid in over 17 years becomes £19,930 in a junior ISA at 18, or £24,912 in a junior SIPP. Left alone to 60, that SIPP reaches £511,675. Restart contributions at 22 and it reaches £661,264, against £529,012 for the ISA. Raise charges to 1.2% and £181,915 disappears. Double the contribution to £100 a month and the pot hits £1,322,529 — which 3% inflation reduces to £231,211 in today's money.(00:00) I think I've been doing this wrong(01:12) The junior ISA as it stands(02:32) Chris makes the case for the ISA(05:02) Would an 18-year-old actually blow it?(06:31) The tax relief is worth £82,000(07:20) Junior ISA against junior SIPP at 18(09:01) What happens if they restart at 22(09:40) When can they actually access a pension?(10:30) What charges do to all of this(13:00) Only 23% of UK workers are on track for a moderate retirement(15:43) What £100 a month becomes(17:36) The inflation problem nobody talks about(20:00) Tax on the way out(20:49) What Chris is doing(21:23) What I've decided to doFull tables and charts, at both contribution levels and both charge scenarios, in cash and in today's money: [Substack link]Retirement Living Standards figures from Pensions UK, 2026 update, calculated by the Centre for Research in Social Policy at Loughborough University.Neither of us is a financial adviser and none of this is financial advice. All projections are illustrations based on stated assumptions, not forecasts. Investment returns are not guaranteed and tax rules change.