There are fears children could struggle in the classroom in later years
The development of toddlers' brains can be set back by decades if they are not adequately stimulated in the years before starting school, according to neuroscientists and charity workers.
Experts are calling for more to be done to make the most of the "lightbulb" years, when toddlers' brains are developing rapidly.
A report from University College London's Institute of Child Health and the charity Save the Children has revealed toddlers' brains form connections at double the rate of adults.
If children fail to develop adequate language skills early on, it can leave them struggling to learn in the classroom during later years.
Professor Torsten Baldeweg from the UK's Institute of Child Health said: "It is precisely this period where we have explosive brain growth, where most of the connections in the brain are formed".
"We need input to maintain them for the rest of our lives. And we know that if these connections are not formed they, to variable degrees, will suffer longer-term consequences to their physical, cognitive but also emotional development".
Save the Children has warned that every nursery should have a qualified teacher to help children develop their speech and language.
Last year almost 130,000 children in England were falling behind with language abilities before they even reached school, the charity said.
This means six children in every reception class struggled with their early language skills, it said.
Steve McIntosh from Save the Children says: "All the evidence shows that children's pre-school years are amongst the most rapid and active periods of brain development, which makes it absolutely vital that we get early learning right".