What's the idea of adding plus possible tax relief?
For fresh MA and SA deposits, which this would be, tax relief is
possible. It certainly depends on whether the child has Singapore taxable income.
Also protected from the kid's dire needs?
No, not all dire needs. MA is available for all qualified medical expenses in Singapore (one set of dire needs) and is paid out to the child's CPF nominee (such as the child's spouse), serving as a form of life insurance -- another dire need. SA is available for hardship withdrawals even prior to age 55 (terminal illnesses, etc.), another set of dire needs, and of course nomination as with MA. Moreover, since these future money uses are better secured earlier, the child has greater freedom to adjust current spending, saving, and insurance patterns now, all of which help defend the child better against dire needs. There are also a few situations involving children who are reckless, and so defending their futures from themselves is quite important. Sad, but occasionally true.
Maintaining at least adequate liquidity and cash flow is undoubtedly important, but the key word is adequate. If "maximize liquidity at all times!" were a valid, reasonable financial objective then nobody should ever buy any homes, especially not any HDB leaseholds, for example. Of course if you are going to accept a reduction in liquidity you should be reliably rewarded for doing so. In many of the scenarios described you and/or your child will be well rewarded.
Please note that "child" does not equal "minor." Nobody ever qualified this by saying "minor child." There are some additional considerations that apply to minors receiving CPF deposits.