So I've just had a quick read of that particular thread. It appears that there is one poster who claims to be a former DM who is talking about a specific type of trust.
It's interesting that what this person says is directly contradicted by the guidance given by the DWP in the advice to Decision Makers:
ADM Chapter H1: Capital (publishing.service.gov.uk)
Ownership of capital of a child or young person
H1077 Capital owned either legally or beneficially by a dependent child or qualifying young person is not to be included in the capital of the claimant. However, the DM may still need to make enquiries about such capital if it appears to be owned by the claimant but is actually beneficially owned by a child or young person for whom they are responsible.
H1078 Children and young people may not be the legal owners of the capital of which they are the beneficial owners. This is because businesses, such as banks, will not enter into a contract with them. If they are the beneficial owners and not the legal owners their capital will be held on trust by another person.
Universal Credit Decision Makers (DMs) will look at the overall situation to see if you have done anything that may be described as "deprivation of capital".
If, all of a sudden, you open a child savings account just as you are made redundant and transfer all your savings into it then they will likely count that as deprivation.
In contrast, if you were to open a child savings account today and regularly pay money in to the account each year then, if you did go onto Universal Credit in a few year times, and you paid a similar amount into your child's savings account at that time then you have not changed your regular behaviour so it would be difficult for them to prove that it was done for the purpose of claiming benefits.
But any money that goes into the child's savings account is held on trust for the child. If you wish to take money from the account then it must be used for the benefit of the child. This can certainly included things like paying for private education.
The onus of proof is on the DM to prove that the claimant’s intention was to increase or retain their entitlement to benefits.