asked why, in view of Article 6 of the Royal Warrant, an instruction has been issued that in the event of a man undergoing treatment and in receipt of allowances becoming the father of a child ten months or more after the commencement of treatment, no allowance shall be payable for such child?

The purpose of treatment allowances is to meet the circumstances and family obligations of the patient at the time that treatment commenced. Article 6 of the Royal Warrant has, in fact, been generously interpreted so as to permit of allowances being paid for all children alive at the commencement of treatment or born within nine months after treatment commenced (notwithstanding that such children were not pensionable), but the allowances are not properly payable in respect of children born at a later date.

Do I understand from that that a pensioner's obligations are not increased during treatment if an additional child is born?

No, the answer is as given, but the fact remains that these men receiving treatment get more generous treatment in a way than the pensioners themselves.