The number of children with illnesses or disabilities aged nine years grew by 13% between 2008 and 2018, according to new research by the Economic and Social Research Institute.
The findings, which are based on data from the Growing Up in Ireland study, also show that families eating together has become less common, declining from 72% to 67% in that time.
Mothers and fathers have reported greater closeness to their children, but mothers also reported increased conflict.
Nine-year-olds are broadly positive about school, with an increase over time in the proportion always liking it (from 27% to 33%).
However, the ESRI has said that attitudes to school subjects, including reading and Maths, remain largely unchanged.
The study has found that nine-year-olds typically have two or three close friends, but the numbers with a larger network of six or more friends has increased over time (from 17% to 25%). Around a quarter see their friends outside school almost every day.
Changes are evident in children's pastimes, with a decline in those taking part in sports between 2008 and 2018 (from 44% to 34% playing sport almost every day) and cultural activities (such as music or dance lessons - from 47% to 44%).
There was a significant increase in the proportion of nine-year-olds with their own mobile phone (from 44% to 54%) and according to the study, there has been a marked shift in the amount of time watching television towards time on other digital devices.
It has pointed out that those spending more time watching TV and using computers are less likely to engage in sports, reading for pleasure and cultural pursuits.
Owning a mobile phone is also associated with less time reading and lower levels of involvement in cultural activities, according to the ESRI.
On the subject of gender differences, the study found that the social worlds of nine-year-olds are "quite different for girls and boys" and these gender differences persist over time.
Girls have closer and less conflictual relations with their parents than boys but have smaller friendship groups and see their friends less often.
They are more likely to read for pleasure and engage in cultural activities but less likely to take part in sports. They also spend less time on digital devices than boys.
Nine-year-old girls are also more positive about school overall but less positive about Maths, and the study has shown gender differences in attitudes to Maths widen over time.
The study found children's lives are strongly influenced by the socio-economic situation of their families. More parent-child conflict is found and children tend to have smaller friendship groups where families are under financial strain.
Children from more advantaged families are more likely to be involved in sports and this social gap widens over time. Social background differences in reading for pleasure become more pronounced over time, with a decline in daily reading for all children except those with graduate parents.
The ESRI said the findings have significant implications for policy.
Gender and social background differences in children's activities emerge early, suggesting the importance of early years provision in providing access to a variety of engaging activities for girls and boys and across all social groups.
It said schools can play an important role in encouraging physical exercise among children, but also points out the need for community-based facilities, given the constraints for small schools in provision of extracurricular sports.
'Concerning trends'
Report author Professor Emer Smyth said there are concerning trends regarding children’s involvement in sports, cultural pursuits and reading - activities that enhance their development.
"Subsidised provision of sports and cultural activities for more disadvantaged groups could help encourage participation. Continued efforts on the part of schools and libraries will be crucial in trying to reverse the decline in reading for pleasure found among many groups of children," she said.
The Growing Up in Ireland study is produced in partnership with the Department of Children, Equality, Disability, Inclusion and Youth (DCEDIY).
Prof Smyth said the research shows "quite concerning trends in children's activities outside of school".
Speaking on RTÉ's Morning Ireland programme, she said it is difficult to find a single reason but "we do see a shift in the kind of screen time, an increase in the proportion of mobile phones and a shift away from television to other devices".
"We see a fall-off in participation in regular sport, a decline in pursuits of cultural activities like music and drama classes and a fall-off among most groups of children in reading for pleasure," Prof Smyth said.
"We see they have good relationships with their parents, the majority report getting on very well with their mother and with their father. Although that has declined slightly over time, it is still very high," she added.
Prof Smyth highlighted the importance of research on Irish children.
"I think it is really important that we have this evidence on Irish children, that we're not just reading British or American studies and extrapolating and assuming that Irish children are the same, because they're not," she said.
