Please tell me the symptoms of mental retardation in a toddler?

Definitions. Generally, global developmental delay is the term used at that age. If testing shows a toddler's overall functioning to be < 50% of what it should be for his age, he is at risk for intellectual disability ( formerly mental retardation) when tested at age 6. Another clue is lack of significant progress over time, despite having early intervention services to increase his rate of development.
Delayed development. Sitting up, crawling, walking and speaking words all delayed significantly, bearing in mind that there arae wide differences in normal toddlers.