yes i agree those ONS charts are hard work and I have been looking at them for the last 2 years. I had a look at the twitter handle and it seems the number of 145 children deaths is coming from Covid mentioned on death certificate rather than Covid being the actual cause of death.

A more useful way to cut through the background noise is to look at all cause mortality in different years and this gives some interesting data. Following are the number of deaths in England and Wales in children aged 1-14 in the last 5 years ( I got these numbers by just manually adding up the rows on the ONS data)

2017 943
2018 961
2019 934
2020 832
2021 812

so total number of deaths in children in this age group has actually fallen over the last 2 years