Children with weakened axial muscle tone face various problems every day. One is maintaining a stable body posture, which limits their participation in activities and games with peers. The study aimed to assess balance parameters in children with weakened axial muscle tone who underwent sensory integration therapy (SI). The study group consisted of 21 children (divided into three age groups) referred by a doctor for therapy. Methods: The ZEBRIS platform was used to measure the balance parameters (MCoCx, MCoCy, SPL, WoE, HoE, and AoE). The study was conducted twice: before and after two months of sensory integration therapy. The results were compiled using the TIBICO®Statistica software version 13.3.0. Results: After the SI program, statistically significant changes were observed in the values of MCoCy_oe, WoE_oe, AoE_oe in the group of four-year-olds, MCoCX_ce in the group of five-year-olds, and in SPL_ce and AoE_ce in six-year-olds. A statistically significant, highly positive correlation was observed between body height and changes in SPL_oe, HoE_oe, and AoE_oe in the group of six-year-olds, as well as in the case of changes in SPL_oe in the group of five-year-olds. In the group of four-year-olds, a statistically significant correlation occurred only between body height and the change in the MCoCx_oe value. Conclusions: the sensory integration therapy used in the study group of 4–6-year-old children with reduced muscle tone gave positive results in the form of improved static balance and balance.