It is completely unreasonable to compare known deaths with known cases. The reason is we have not done widespread antibody testing and something like 50% of those who got don't even know it. In studies where all people in a given area were tested for antibodies as an experiment, the ratio was about 50 to 1 previously unknown versus known infections. On the other hand, the policy in many hospitals is to call the cause of death Covid-19, even though the person may have the disease but died from some other cause. The most believable mortality that I have heard reported is more like 0.1 - 0.3%.
If all 16 of your grandchildren contracted Covid-19, the chances of any of them dying are vanishingly small because young, healthy people don't die from it. It is only old people with other contributing factors like me who die. I have read that 50% of the fatalities so far occurred in nursing homes or similar facilities. It is noteworthy that these people are among the most protected of all populations.