Participants in this arm will receive the MSE-PEACE intervention, a family-centered multi-sensory environment program designed for children with developmental disabilities and their caregivers. The intervention includes 10 sessions delivered every 2 weeks, with each session lasting approximately 60 minutes. Sessions take place in a specialized sensory therapy room and are guided by certified occupational therapists.

The intervention combines sensory-based activities with active parent-child co-participation. Each session is tailored to the child's sensory profile and developmental needs. Parents are engaged in goal-setting, activity participation, and follow-up support, including suggestions for home-based sensory activities and environmental adaptations. The program aims to improve children's functional engagement and emotional regulation, while enhancing caregiver empowerment, parenting competence, and family well-being.

The MSE-PEACE (Multi-Sensory Environment-Parent Empowerment and Child Engagement) intervention is a family-centered, therapist-guided sensory integration program specifically developed for children with developmental disabilities and their caregivers. Unlike traditional child-only sensory therapies, this intervention actively involves parents in all stages-assessment, goal setting, activity participation, and follow-up.

Each participant dyad (parent and child) attends 10 biweekly sessions (60 minutes each) in a structured sensory therapy space equipped with adjustable lighting, tactile materials, auditory inputs, and other multisensory tools. The intervention is tailored to each child's sensory processing profile and emotional regulation needs, while promoting parent-child co-regulation, bonding, and collaborative engagement.

Occupational therapists facilitate the sessions using individualized strategies to support child-led participation and empower parents with real-time coaching,

The Pediatric Volitional Questionnaire (PVQ), adapted from the Volitional Questionnaire, is used to assess a child's motivation and engagement in different environments. It consists of 14 observational items such as curiosity, task initiation, persistence, and problem solving. Each item is scored on a 4-point scale from "Passive" to "Spontaneous." The scores range from 14 to 56, higher scores mean better engagement. Observations are conducted during 15-30 minutes of free play in natural settings (e.g., therapy room, playground, or home). The PVQ has demonstrated strong reliability and validity in children with developmental delays, with an item separation reliability coefficient of 0.97. This study uses the PVQ to evaluate changes in children's volitional behavior and functional participation before and after the MSE-PEACE intervention.

The Short Sensory Profile 2 (SSP-2) is a 34-item caregiver-reported questionnaire used to evaluate sensory processing patterns in children aged 3 to 14 years. It assesses four sensory quadrants: sensory seeking, sensory avoiding, sensory sensitivity, and low registration (observer). Caregivers rate each item based on the child's typical behavior in daily life using a 5-point Likert scale (1 = Almost Never to 5 = Almost Always). Higher scores within each quadrant indicate greater difficulties in sensory processing according to age norms.

The Chinese version of SSP-2 has been translated and validated in prior studies, showing strong internal consistency (Cronbach's α = 0.949). This study uses the SSP-2 to assess changes in children's sensory processing patterns before and after the MSE-PEACE intervention.

The Emotion Regulation Checklist (ERC) is a 24-item parent-report measure used to evaluate children's emotion regulation abilities. Parents rate how frequently their child demonstrates specific emotional behaviors in daily life using a 4-point Likert scale (1 = Never to 4 = Almost Always). The ERC includes two subscales: Emotion Regulation (ERC-ER), which reflects a child's ability to understand and express emotions appropriately, and Lability/Negativity (ERC-L/N), which reflects emotional dysregulation and instability. Higher ERC-ER scores indicate better emotion regulation, while higher ERC-L/N scores indicate greater emotional dysregulation.

The Chinese version has shown acceptable internal consistency, with Cronbach's α values of 0.88 (ERC-ER) and 0.64 (ERC-L/N). This study uses the ERC to assess changes in children's emotional self-regulation following the MSE-PEACE intervention.

The Parent-Child Relationship Inventory (PCRI) is a 78-item parent-report questionnaire designed to assess the quality of the parent's relationship with their child. Items are rated on a 4-point Likert scale from "Strongly Agree" to "Strongly Disagree," including some reverse-scored items. The scale consists of seven subscales: Support, Satisfaction, Involvement, Communication, Limit Setting, Autonomy, and Role Orientation. Higher scores indicate a more positive perceived parent-child relationship.

The Chinese version of the PCRI was translated and back-translated by bilingual professionals and reviewed by experts in occupational therapy to ensure conceptual and linguistic equivalence. It was pilot-tested with caregivers of children aged 3 to 6 to ensure clarity and cultural relevance. Internal consistency ranges from 0.59 to 0.82 across subscales, with acceptable reliability for most dimensions.