Nearly two-thirds (62%) of children adopted in Britain last year were aged between one and four, official figures showed today.
The 2011 figure was an increase on the previous year, when one to four-year-olds made up 58% of adoptions in England and Wales, the Office for National Statistics said.
There was also a 6% increase in the overall level of adoptions, with 4,734 in 2011 compared with 4,481 in 2010.
The percentage of children adopted who were born outside marriage increased slightly to 82% last year, up from 80% in 2010.
Adoptions also increased in Scotland between 2010 and 2011 by 6%, from 466 in 2010 to 494 in 2011.
No figures were available for Northern Ireland.
In a reverse of last year's figures, 49% of children adopted in 2011 were male and 51% were female. Since 1998, the number of male and female adoptions has been fairly even, the ONS said.
The proportion of adopted children aged one to four has steadily increased since 1998.
Last year's figure of 62% is almost double the proportion of 34% in 1998.
Meanwhile, the proportions of adoptions of other age groups has decreased.
The percentage of under-ones being adopted was 5% in 1998, down to 2% in 2011.
For children aged between five and nine, the proportion has decreased from more than a third (36%) in 1998 to just under a quarter (23%) in 2011.
The percentage of children between 10 and 14 being adopted has more than halved from over one in five (21%) in 1998 to one in 10 (10%) in 2011.
The percentage of adopted children aged 15-17 has decreased to 2%, from 5% in 1998.
In total, the number of babies under one year old adopted decreased from 95 in 2010 to 76 in 2011, the ONS said.
Last month, Prime Minister David Cameron unveiled plans to radically speed up the amount of time it takes to place children with potential adopters.
Youngsters will be able to move in with their possible future permanent families before lengthy legal procedures are finalised, Mr Cameron said.
Mr Cameron hopes the Fostering For Adoption scheme will give children a better start in life by ensuring they have a stable home as quickly as possible.
Under the plans, men and women who have been cleared as adopters can become a child's foster parent until they are legally allowed to adopt them. Now, local authorities generally wait until court orders are made before beginning their search for a permanent home.
The move will not pre-empt any legal ruling, meaning the youngsters could be returned to their birth parents or other carers.
But the Government hopes it will mean the interests of the children are put first.
A Department for Education spokesman said they were committed to overhauling the adoption system to make it more effective.
He said: "Adoption can be a lifeline for vulnerable children and we are determined to see more children considered for adoption, particularly those who may previously have been overlooked.
"We are committed to overhauling the entire adoption system to give more vulnerable children the chance of a loving, stable home with adoptive parents. That's why we are changing the law and calling for urgent action - both from local authorities and from potential adopters - to reduce barriers and delay in the adoption process.
"We want to create a more effective and user-friendly adoption system - a system which is truly fit for purpose."