The presentation of ADHD subtypes and the most common comorbid disorders change over time and by developmental stage. The most common comorbid disorders in early childhood are oppositional defiant disorder (ODD), language disorders and enuresis. Many children with ADHD have a specific learning disorder 20.
http://www.caddra.ca/pdfs/caddraGuidelines2011Chapter02.pdf
ADHD and Depression. ADHD and major depression (MD) are common, disabling disorders that afflict both children and adolescents. Studies have found that between 5% and 40% of children and teens with ADHD meet criteria for MD. Furthermore, family members of children with ADHD are more likely to have a history of MD.
http://www.medscape.org/viewarticle/555748_3
Children with ADHD and anxiety disorders (or with co-occurring depressive disorders) may also display a general lack of motivation and a sense of learned helplessness, or the belief that their actions and intentions do not truly make a difference in their lives.
https://www.mentalhelp.net/articles/adhd-comorbidity/
■ 10 50-90% of children with ADHD have at least one comorbid condition; ■ Approximately half of all children with ADHD have at least two comorbidities 10; ■ 260 85% per cent of adults with ADHD meet criteria for a comorbid condition.Comorbidity contributes to the failure to diagnose ADHD in adults and children.
http://www.caddra.ca/pdfs/caddraGuidelines2011Chapter02.pdf
ADHD with a comorbid condition may be indicative of one disorder being an early manifestation of the other, or that development of one disorder increases the risk for the other. Another possibility is that one disorder is a subtype of the other (conduct disorder and ADHD may be a subtype of ADHD).
http://www.caddra.ca/pdfs/caddraGuidelines2011Chapter02.pdf
Comorbidity is the medical term for two or more disorders that occur at the same time. In general, individuals affected by ADHD often have other behavior disorders that impact their ability to function successfully.
https://www.mentalhelp.net/articles/adhd-comorbidity/
It is very important to distinguish between true anxiety disorders and those children who are experiencing anxiety in response to ADHD, because the treatment options are very different. 1  Stimulant medications, while helpful for ADHD symptoms, may actually worsen the symptoms of true anxiety disorders.
https://www.mentalhelp.net/articles/adhd-comorbidity/
Depression. 10 to 30% of children with ADHD have a co-occurring mood disorder such as depression. Although many depressed adults move, think and talk slowly, children often demonstrate different symptoms when depressed. 1  For example, children may show extreme impulsive and hyperactive behavior as well as irritability.
https://www.mentalhelp.net/articles/adhd-comorbidity/
One of the possibilities is that the individual has comorbid disorders of ADHD and Specific Learning Disorders (SLD). Indeed, research indicates that the comorbidity of ADHD and learning disorders is high. Chapter 2 2.5 Comorbidity of SLD and ADHD The comorbidity range has been suggested to be between 31% and 45%. One out of every three children with ADHD also have an SLD 264.
http://www.caddra.ca/pdfs/caddraGuidelines2011Chapter02.pdf
Learning Disorder. Over ½ of all children with ADHD also have a learning disorder. ADHD, though it affects the ability to learn, is not a true learning disability. So, treating the symptoms of ADHD will not correct any learning disorders that a child may have.
https://www.mentalhelp.net/articles/adhd-comorbidity/
what are comorbid diseases in infants and toddlers
Comorbid diseases in infants and toddlers causes Oppositional defiant disorder, language disorders and enuresis. Oppositional defiant disorder, language disorders and enuresis are comorbid diseases in infants and toddlers.  