Severe trauma and inappropriate sexual behaviour among pupils goes untackled in some schools because they cannot afford to run schemes that are proven to help, Ofsted warned this week.
Inspectors have called on the Government to question local authorities about the support they give to heads who regularly exclude pupils aged four to seven.
They also want government guidance for schools "urgently" on how best to respond to inappropriate sexual behaviour among the age group.
Heads in the study reported a lack of interest from social services when they raised their concerns.
The report found the use of Circle Time and the social and emotional aspects of learning (Seal) were particularly effective in reducing exclusions. Nurture groups were also successful, but many schools said they could not afford them.
Ofsted visited 30 schools that had excluded several young children and another 27 nearby schools where teachers had not used the sanction. Inspectors also went to 12 schools that had excluded only one young child, and 10 authorities with high exclusion levels.
More than half of the schools visited were among the most deprived in the country - many pupils came from troubled families.
Ofsted reported "weaknesses" in the way exclusions information is analysed by the Department for Children, Schools and Families in an overall way, rather than for individual schools.
The DCSF should:
Analyse exclusions data annually school by school basis and question local authorities about the support they offer primaries.
Investigate mental health support for children who have suffered trauma; evaluate nurture groups; produce guidance for governors.
Local authorities should:
Analyse closely the exclusions of children and support schools; ensure referrals are taken seriously.