Triplets develop more slowly than single babies and twins, a study says.
Mothers need to spend time stimulating babies, the study says
Researchers analysed the cognitive development of 23 sets of triplets, 23 sets of twins and 23 singletons.
The team from Bar Ilan University in Israel found by the end of the first year triplets showed poorer development in words, gestures and basic play.
The findings in triplets was because mothers could not devote as much time to stimulating their children, the report said.
Instead, nearly all their time was taken up attending to the physical needs of the children.
Mother's also tended to engage less and show less warmth to the triplet that was weakest at birth.
This child showed the least cognitive development, which includes perception, reasoning and creativity, than their siblings, according to the study.
Researchers also found parenting stress in families raising triplets was "especially high", particularly in the first six months.
However, the team said as triplets grow older they may benefit from interaction with each other.
The findings came as the number of triplet births has increased tenfold since 1980 in industrialised countries.
In England and Wales, 15 out of every 1,000 births are to more than one child.
The report contradicts previous research, which has suggested the development of twins was stunted too.
Report author Dr Ruth Feldman said the reason for the difference between twins and triplets was the "cut-off" point had been reached.
"Below this cut-off, we think, the child may not receive the kind or individual parenting he / she needs for optimal growth.
"The ratio of child-to-parent is not in favour of the parent, and parents report that this one more infant makes a difference between manageable and unmanageable parenting situation.
"One mother in our study who had both twins and triplets was especially vocal about this difference.
"We had, for instance, several cases of triplets who did not leave the house for the first several months of their lives, just because parents could not handle going up and down the stairs with three babies.
"No such thing was ever reported for twins."
Dr Feldman said governments should consider offering some kind of support to parents of triplets.
And she urged parents of triplets to try to get as much help as possible.
Helen Forbes, director of the Twins and Multiple Births Association (Tamba), said it was not surprising that triplets develop more slowly as they are born six weeks earlier than single babies on average.
"Triplets are often born prematurely and, therefore, they reach milestones at a later age.
"Of course, the amont of time parents can spend with the children is a factor. But I would urge parents not to be too alarmed."