The new rules are needed but ministers must set out an exit strategy, Sheffield City Region's mayor says.
Sending some children home may be the only way to control infection rates, a former adviser warns.
The council says the restrictions must be imposed earlier to "urgently" bring down case numbers.
Greater Manchester Police says it has issued 52 fines since tier three rules came into force.
The 17-year-old boy was pronounced dead at the scene in east London on Friday night.