This study evaluated whether commonly used household cleaning agents affect the surface microhardness of acrylic and copolyester materials used in pediatric removable appliances and sought to identify safe options for daily home cleaning. Standardized acrylic and copolyester specimens were exposed to a short-term, clinically relevant brushing regimen using tap water (control), children’s toothpaste, liquid soap, antibacterial liquid soap, 20% saline solution, or 20% sodium bicarbonate (“carbonated”) solution. Surface microhardness was assessed with Vickers testing, and surface features were examined by light microscopy. In the acrylic group, antibacterial liquid soap and the carbonated solution were associated with reduced microhardness (Spearman ρ = −0.622 and −0.532, respectively; both p < 0.001) and more pronounced surface alterations. In the copolyester group, antibacterial liquid soap showed a significant inverse association with microhardness in regression analysis (p = 0.032), while the other agents showed no statistically significant relationships (p > 0.05). Clinically, antibacterial liquid soap should be avoided for routine cleaning of both acrylic and copolyester appliances, and sodium bicarbonate–based carbonated solutions may be detrimental to acrylic. Children’s toothpaste and ordinary liquid soap appear to be practical, safer alternatives for daily use.