Adverse life experiences can impact a child's ability to meet developmental milestones. In some instances, development does not keep up with with chronological developmental milestones, resulting in behavioural issues, such as the inability to cope with frustration or change. Often a child's developmental age, which is the age at which they function emotionally, physically, cognitively and socially, is much younger than what we would typically expect.
In brief, this is because when a infant/child does not get access to a safe, predictable and a loving care-giving environment, their brain development is altered and may not go through the normal sequence of growth. From studies into Developmental Trauma when the stress response in children is repeatedly activated then sequential development of the brain is disturbed, where foundation steps are missing and the lower parts of the brain that are responsible for survival functions and emotional regulation are disrupted causing the upper part of the brain to also be effected and this causes other elements to be out of kilter, and this manifests in a variety of behaviours and an impairment of executive functions ie making judgements about what you are experiencing and exercising moral judgement as well as difficulties such as sensory processing disorder, ADHD, cognitive impairment, speech delay etc.
Adjusting they way you see a child, for example seeing their developmental stage as being much younger, you can start to help them meet their needs more appropriately (needs of a much younger child) and fill in skill gaps by letting them practice new skills repeatedly in a safe environment to enhance their developmental progress.
The below image shows a snapshot from a Fagus Developmental profile for a child who is 9 years old. It shows that in the Self-Control social and emotional domain this child's behaviours are typically similar to the behaviours of a child in the Infant Age Range. Their ability to self regulate and control their impulses are very delayed. The objective would be to put a goal in place to teach the child a set of skills around self control to help them to practice and improve their skills in this area, within a safe and nurturing environment. These may involve brain stem and mid-brain functioning and include activities such as yoga and expressive arts. The Developmental Profile can repeated and original goals set reviewed to see whether the pupil has made any progress in this area. Although please be aware this journey may span a number of years.