Abstract:

Introduction:
Up-to-date information on the achievement of developmental milestones in a population of children is important for detecting possible difficulties in child development before they enter kindergarten. Parents begin to notice the risks of developmental difficulties in their children at around 19 months of age, and up to 80% of parents correctly identify abnormalities in their child's development by the age of two years. However, there is a need to find out what the rate of achievement of developmental milestones is in the population of young children. The developmental difficulties that may be indicated by failure to meet developmental milestones lead to possible unhealthy social and emotional development, problematic relationships, and difficulties in the child's later, even academic, functioning. The purpose of this paper is to determine the difficulty and discriminatory ability of developmental milestones for a population of children aged two and three.

Methods:
The study population consisted of 927 2-year-old children (Mage2y = 31,52 months (SDage2y = 3,13) and 304 3-year-old children (Mage3y= 36,78; SDage3y = 1,17). Achievement of developmental milestones in the population of children was ascertained with the Screening of Psychomotor Development 11 (S-PMV11) instrument. It is part of the Method for Monitoring the Development of Psychomotor Function and Screening for Developmental Difficulties, designed to screen for psychomotor development at the 11th Preventive Examination in General Care for Children and Adolescents (©Prof. K. Matulaya n.d. Fund, 2016). Item difficulty was examined through item difficulty index and discriminative ability of items was investigated through upper-lower-index (ULI) coefficient.

Results: The developmental milestones with the lowest achievement rates in both groups of children were the milestones focused on speaking, communicating the need to go to the toilet, and kindergarten readiness from the parent's perspective. Item difficulty ranged from 72-98% for two-year-olds and 83-99% for three-year-olds. We found that the most challenging milestones focused on speech with achievement rates of around 72-75% for younger children and 83% for three year olds, while also achieving the highest discriminative ability.

Discussion:
The developmental milestones corresponded in their difficulty to a logical developmental sequence, with the highest variability in the domain of speech. It is delayed speech that is a significant indicator of developmental variability but also a risk for several developmental difficulties in children aged two and three years. By early identification of developmental risk in children aged two and three and support from the family environment, some problems can be prevented. Problems are most pronounced during the child's integration into the educational process in kindergarten, which may be too late to provide effective stimulation and follow-up care. Achieving developmental milestones based on parental assessment of development may reveal difficulties before entering kindergarten. Many kindergartens list basic mastery of self-care as an entry requirement for entering kindergarten, but the child's speech development also needs to be addressed.

Keywords:

Developmental milestones, developmental difficulties, early childhood, developmental screening.