Early intervention programs aim at improving cognitive and motor outcomes of preterm infants. Intensive custom-tailored training activities are usually accompanied by assessment procedures, which have shortcomings, such as subjectivity, complex setups, and need for structured environments. A novel sensorized system, called CareToy, was designed to provide stimulation in the form of goal-directed activity training scenarios and motor pattern assessment of main developmental milestones, such as rolling activity, grasping, and postural stability. A group of 28 differently skilled preterm infants were enrolled. Acquired measurement data were analysed with dedicated sensor data processing algorithms, along with clinical evaluation of motor ability. High correlation among technically determined parameters and Alberta Infant Motor Scale values was determined by Pearson correlation coefficients. Due to good accuracy and possibility of single motor skill subfield analysis, results confirm system suitability for motor ability assessment. Statistical analysis of inter-motor ability group and inter-training goal data comparisons demonstrate system's appropriateness for goal-directed activity stimulation. The proposed system has evident potential of being an important contribution to the field of infant motor development assessment, expanding accessibility of early intervention programs and affecting rehabilitation effectiveness of preterm infants.