if a child does not have an existing health issues the risk of covid itself is so low that even if the vaccine had no complications the cost of the vaccine itself would probably outweigh the individual benefits conferred to the child. it's very difficult to justify a medical intervention when the risk is so low. if you are taking a more utilitarian view then it is certainly better to be sending vaccines that would be given to children to other countries that currently have a shortage of vaccines for at risk groups.

the UK had a vaccine committee that authored a report on the benefit and risks of giving a vaccine to children. they concluded the benefits outweigh the risks but the benefits are so small that it is impossible to justify taking action.

https://www.gov.uk/government/publications/jcvi-statement-se...