Best place to save a lump sum for our child

eskbanker

refluxer said:
I also suspect that a £16.5k PB holding would see a return of a lot less than 0.9%, too.

Quite possibly but the point is that, as 0.9% is the median average, there's as much chance of beating it as there is of underachieving, regardless of size of holding and duration - larger holdings and/or longer timescales reduce the standard deviation but not the average itself. 

In other words, a large holding for a long time may have, say, an 80% chance of, say, 0.8-1.0% (but 10% chance of less and 10% chance of more), but a small holding or a short time may have, say, a 40% chance of 0.8-1.0% but 30% of less and 30% of more....