This study is a randomized, controlled trial designed to evaluate the effects of transcutaneous tibial nerve stimulation (TTNS), TTNS combined with pocket-sized handheld ultrasound (PHUS), and conventional therapy with PHUS on children with functional constipation (FC). Participants will be stratified into three intervention arms (n=20 per group). FC will be defined based on the Rome IV diagnostic criteria, in the absence of organic or anatomical causes. Participants will be between 4 and 14 years old and will have experienced failure of conservative treatment for at least three months prior to enrollment. The primary outcomes include changes in rectal ultrasound parameters and symptom severity scores. Ultrasound assessments will be conducted by trained clinicians using standardized protocols. Monitoring for adverse events will be performed throughout the intervention phase. Safety considerations include predefined exclusion criteria, such as underlying neurological, metabolic, or cardiac conditions.