I'm widowed and leaving my RSP to my adult children. Until my RSP is collapsed and transferred to them, will the earnings still be sheltered from tax?

Only for a short period  after one's death the RSP remains tax sheltered. It is taxable trust (if it's not closed) in second year following the death of an individual.

For example, at the time of death if one's RSP was worth $80,000 and when it collapsed it was $85,000. The growth of $5000 becomes taxable to the beneficiaries when the RSP is paid to them. This new tax rule give little relief which allows to claim tax deductions if any losses occur due to the RSP declines in value after death.