Implied trust from Death in Service

The trustees of a company’s Death in Service have issued a letter to the deceased’s spouse, confirming 1/3 payment to her, and the balance split between their two children. The letter states these are to be held in trust for the two named children.
For the sake of administration, does she need to arrange completion of a new bare trust deed to invest their monies?

From the tenor of your post I assume that you/your client do not wish to challenge the proposed division, or the “named” beneficiaries?
If so, the terms of the trust should be set out in the Pension/Death in Service scheme - with their Trustees acting, unless/until they agree to appoint substitute trustees, to act on the same trusts.
I fail to understand your reference to a “new bare trust” as this could only arise if both children had reached full age or otherwise complied with the terms of the trust - in which case, why would they need a bare trustee?