People in Wales have been "strongly advised" by scientific advisers to postpone celebrating Christmas together and to put off reunions if possible.
They say families with children should consider "pre-isolating" at home for 10 days before seeing elderly relatives.
The advice is contained in a report by the Welsh Government's Technical Advisory Group (TAG).
Welsh ministers and council leaders have pledged to keep schools open until term ends on 18 December.
But the TAG report says: "Pre-isolation may be a helpful consideration for families with children before visiting older relatives."
Pre-isolating for 10 days would mean pupils finishing school this Friday.
Governments in the four UK nations have agreed to follow similar coronavirus restrictions at the end of December, allowing three households to mix.
The report warns that different generations meeting is "highly likely" to help spread Covid-19.
Increased infections of older people are "likely to lead to higher deaths and hospitalisations after Christmas".
The report says that "pre-isolating" - avoiding anyone outside your household for the virus's 10-day incubation period - "would likely be an effective way of lowering your risk of infecting others".
"If people can avoid seeing others over the Christmas period, perhaps postponing celebrations until later next year or meeting remotely, then this is strongly advised," it says.
As well as families with children, it says people in high-risk jobs, such as factory and care workers, could reduce the risk of transmitting the disease by pre-isolating before mixing with other adults.
Holding the report in his hands during Tuesday's First Minister's Questions, Mark Drakeford said that while a "period of restraint for 10 days before the Christmas period would be to the advantage of all families" it was still better for schools to remain open until the very last day of term, when possible.
"The real problem is is that we do not have confidence, from the behavioural evidence, that if children are not in school, that they were simply being kept at home and kept away from the contacts that would otherwise create greater risk," he said, answering a question from Plaid Cymru leader Adam Price.
"The fear is is that children who are not in school will be in even riskier environments."
Earlier, Health Minister Vaughan Gething warned the Welsh Government had "difficult choices" to make about Covid rules after Christmas.
He said Wales was the only part of the UK where figures were not falling at the end of November and ministers are considering whether new restrictions will be needed after the festive period.