Personally I would not overlook or dismiss seemingly unrelated circumstances such as a child:
- choosing a friend who hurts (bites) them,
- dumbing self down (pretending they cannot read) in order to fit in,
- engaging in potentially unsafe behavior (open scissors).
A bit of negativity and/or self-punishment may be creeping in.

As you mentioned having a baby in the past year, I would redouble efforts to make sure the three-year-old has plenty of positive parental attention and feels supported and encouraged in asking questions, receiving answers, and continuing to develop academic and social skills.

Regarding the COVID-19 vaccine, as it is an experimental mRNA injection (not an attenuated virus), have you read the Pfizer factsheet for Healthcare Providers, 30-page downloadable PDF? COVID-19 has a better than 98% recovery rate. Early outpatient treatments are especially effective, and have been outlined at recent Senate Hearings. A few links:
1) Senate Hearing Nov 19, 2020
2) Senate Hearing Dec 8, 2020
3) NIH paper, Feb 10, 2011 called "Ivermectin The WonderDrug... "
4) NIH paper, Aug 22, 2005 stated "Chloroquine is a potent inhibitor of SARS coronavirus infection and spread"
5) Peer-reviewed study published Dec 3, 2020