Thats all good and "theoretically" correct but can you show me a simple fund which someone can invest in and potentially leave alone

I looked at - the following which people could have invested in

Fund Inception Return since inception

L&G Global 100. 2002 357%
Vanguard Global Small Cap 2009 356%
iShares Global 100 2000 343%

So whilst this is within 25 years and thus your point correct, it forgets the fact that despite suffering 2 of the catastrophic downturns (Tech and GFC) large caps pulled back whilst small caps started at the favorable position just after the GFC.

The major small cap fund around 2000 was the old F&C Global smaller companies which lags behind somewhat

Interesting your analysis was with US equities only.
The visualizer with your dates also shows that
Gold was better than the US stock market as a whole with a smoother ride.
REIT's even better
That is the same saying that a UK property was even better - especially as I bagged a 4x in October after investing in 2009

Realism has to play a part somewhere

My daughter’s JISA is 10% in a FTSE All Share Index and 90% in L&G international index. So not much different to a straight global tracker. The almost non existent cost of holding those two on HL influenced the specific fund choices.

Not much point in doing anything else, who knows who the winners will be over the next 2+ decades. Yesterday’s winners have neither fundamentals nor momentum in their favour, and using actives would require active management on the part of the one managing the account also. And I wouldn’t want to risk getting it wrong on someone else’s behalf.

So if using ETFs I would probably just stick it all in something like VWRP or SSAC.

There is no hard long term evidence to support trying to do anything more adventurous.

It's impossible to predict the future so you do the best you can, the important thing is to do something. I bought FCIT for my son's CTF when he was a few days old and have continued buying for the past 17 years, it's done well. His next two largest holdings are CTPE and SMT.

A global accumulation ETF (no OEICs) would be my first choice. Whether that be all-world or developed world - In other words; VWRP or VHVG.

Personally, I would go for VHVG (developed world) as the fees are much lower. Then leave it alone.

I'd also be thinking about platform fees, flat fee for ETFs or ETFs for free and also where the platform fee payment is going to come from, if required.

with 12+ straight years ahead bonds for a 5 year old sounds crazy to me. If plans for future schooling then a few years prior it could be reviewed to de-risk what is required.

Lucky kids.

It would have been helpful if you had told me in 2007 that the S & P was the place to be for the next 17+ years. Also, I can't recall your own funds being S & P heavy.

My son has a six figure portfolio when the average CTF is about £2,000, and I know that some of his friends' parents haven't added anything, these children have about £500 to look forward to. But there you go, one does one's best and he isn't complaining.