I’ve only looked at the data for literacy and its impacts on life outcomes. (I do charity in that space.) Something like being 6 months behind in third grade can materially predict high school graduation rates, SAT scores and incomes. Even if one controls for gender, race and income.
Even the 12 year olds I work with who had many years of schooling have had to readapt to meet (greatly relaxed) expectations for in person instruction with several missed months. A whole bunch of 2nd graders with a wasted end of Kinder and 1st grade year is going to be chaotic.
Depression is on a big swing upwards. And there's kids in difficult situations who are not receiving help from caring teachers and social workers. There is going to be impact that lasts for a long, long time.