O/P Appeal - claimant under age 16 at time of o/p

Client being pursued for O/P that occured whilst under age 16 - his mother did not disclose that he had gone into Residential Care .

Whilst I am ploughing through Sweet + Maxwell re : O/P Regs is there anyone with a legal qualification that can point me in right direction to find Regs or can they advise me - some initial questions that are popping into my head are :
1) Does the duty to disclose apply to anyone under age 16 ?
2) Is ‘claimant’ is defined ?
3) The DWP have a formal process for setting up an Appointee - Is there a different process for setting up a parent/responsible adult for children under age 16 ie : is it automatic when someone applies for a benefit for a child ? If so , are they treated in the same way as an ‘Appointee’ as far as legal duties and responsibilities are concerned ?
Thanks

This was obviously a DLA claim as there is no other benefit that can be paid to someone under 16. I’ve never come across a case where benefit was claimed by a child, as opposed to on his behalf by a parent.

Reg 43 of the claims and payments regulations imposes a duty on the SoS (“he shall appoint…a person”) to appoint someone to exercise al the child’s rights and to receive and deal with any sums paid -  normally a parent.

The appointment lapses if the child is taken into the care of a local authority.

The normal rules for appointees may apply - that the acts of the appointee ar attributed to the principal.

Thanks Adriadne ,
I’m interested in your comment re :  Reg 43 - is the parent/guardian set-up in the same way as an Appointee ? An Appointee is set-up by the DWP following an application from a person/corporate body , which is then subsequently approved by the DWP after interviewing all parties concerned however , Reg 43 states if SofS receives a claim from a person under age 16 , “......shall appoint ....and the person so appointed , having given an undertaking ......”  - one requires permission , the other is imposed .

In response to your first sentence , the ‘child’ did not claim - his mother claimed on his behalf and received the benefit . The point being he was under age 16 and I’m trying to find , if it exists , a legal principle similar to the ‘legal age for criminal liability’ ! 
In the world of Social Security , does the legal duty that you have highlighted ie :  “the acts of the appointee are attributed to the principal” , apply regardless of age of the principal ie : it applies to a child under age 16 ?  How can a child protect him/herself from acts of an Appointee ?

Reg 33 deals with ‘Third Parties’ and Para 3 seems to include Reg 43 - not sure from first reading the extent of this ??

Any thoughts please .