Fewer toddlers in Lincolnshire reached key developmental milestones during the first year of the coronavirus pandemic, figures show.
Charity Action for Children has called for urgent investment to prevent a national "childhood crisis", adding that the pandemic meant youngsters spent critical development time isolated and unable to socialise normally.
At the age of two, children are invited to undergo a developmental check to see how they are progressing mentally and physically.
The comprehensive check sees health visitors assess the child's communication, social interaction, problem-solving, fine motor skills (such as holding objects and drawing) and gross motor skills, such as walking without falling and kicking a ball.
Data from the Office for Health Improvement and Disparities shows 82% of Lincolnshire children reviewed met or exceeded expectations in all five areas in 2020-21.
That was down from 86% the previous year.
Across England, the proportion of toddlers achieving in all areas fell slightly to 82.9% from 83.3% the year before.
The biggest decrease was seen in the development of personal and social skills, which dropped from 93% to 90%.
Imran Hussain, Action for Children's director of policy and campaigns, said it was deeply worrying to see so many toddlers falling behind in their development.
He said the pandemic had worsened existing problems, adding: "We know that the first few years are critical to a child’s development so the fact that they have spent the majority of this precious time unable to socialise with family, spend time with other children or enjoy normal levels of play has been devastating.
"Our frontline staff see this every day with children of all ages struggling with their speech, behaviour, education and social skills."
The figures show in Lincolnshire, around 95% of youngsters were on track with their fine motor skills, while 92% had adequate gross motor skills.
Problem-solving was on target for 92% of youngsters and 86% were above or exceeding expectations around communication skills, with 91% able to socialise at an expected level.
A Government spokesman said it was committed to ensuring every child has the best start in life, adding: "The NHS, local authorities and health visitors are working hard to reinstate services to help families get the support they need, and the Public Health Grant will continue to ensure investment is made in prevention and frontline services like child health visits."
The recent Budget saw the Government announce a £500 million funding package to improve support for families, including £80 million for a new network of family support hubs across 75 local authorities.