Wex - I am guessing you have already addressed this, but maybe just review who the trustees would be, and whether there would be any high costs (eg if a solicitor is the trustee), as that would reduce the inheritences.
My DC inherited 2 years ago from a cousin of mine. DS got his when he was just 18! Fortunately he is v sensible and with our guidance is drip feeding it into a S&S ISA, with pots of money in 1/2/3 yr accounts to feed this.
DD is 16.5, and was the only one of 9 beneficiaries under 18. Since the solicitors were executors, they also became trustees, but fortunately they asked DH and I to take over that role. It took from Feb (when estate was finalised) to Nov to get the transfer sorted (crap solicitors!) and in that time they took a reasonable amount in fees, plus also took some of the final lump sum to set up the 'trust' account within their accounting system.
DH and I can afford to cover the deductions so DD doesnt lose out, but I dread to think what the costs would have been if the money had stayed with the solicitors for another 18mths till she turns 18.
We have put 23 on our own wills, with DC as executors at 18, plus SIL, so if anything happens to us whilst they still young, SIL would hopefully manage the trusts until they are old enough to manage the money.
There are a lot of comments on DC not being able to manage money at 18, which I can understand. However, in my DC case, the inheritence was a surprise and my cousin didnt know them well enough to realise they could inherit young (altho his solictor was at fault I think for not advising a minimum age in his will).
Our situation is slightly different to DC inheriting from parents, as we still alive, but we have used it as a springboard for much talking about money, investments, not wasting it, house deposits etc. Hopefully they will therefore be more savvy when older than their friends, as they are learning how to manage money early.