I agree with DannyBoyD — should be fine.
But:
(a) Make sure the trust arrangement is propertly documented. Don't expect DSP just to take your word for it that this is trust money; have a copy of the will/correspondence/whatever paperwork exists in connection with the setting up of this arrangement to show them.
(b) Keep scrupulous records — a note of the purpose of every withdrawal from the fund, plus if possible evidence that the money was spent for the purpose for which it was withdrawn. This is not just a matter for proving the genuineness of the arrangement to the DSP but more broadly, of being able to show, if it's ever called into question, that you carried out your responsibilities properly. You'd be suprised how often these arrangements can go sour. Keep the records for at least 6 years after the last shilling has been spent or the last child turns 18, whichever happens later.
You talk about using the money for "day to day expenses". Obviously I don't know any of the circumstances here, but be careful about using the money in ways which in fact primarily benefit the children's surviving parent or their guardian. Don't, for example, use it to reimburse a parent/guardian for a share of grocery bills, or of their rent, on the basis that they are feeding/housing the children. Feeding/housing children comes as standard with being a parent or guardian, and children are not normally expected to pay for their own meals or accommodation. As long as the children are under age keep the money for things that the parent/guardian can't, or couldn't reasonably be expected to, pay for, and that would be of benefit to the children.