Thermochromic (TC) pigments offer significant potential for functional and aesthetic design of smart textile materials. In this study, TC (blue and red) pigments were applied to cotton fabrics and printed on especially designed childrenswear by flat screen printing technique. The antibacterial and ultraviolet protection functionalities have been implemented into the fabrics under study by using selenium nanoparticles. The factors affecting the printing process were studied and the optimum formula was screen printed to produce the pattern’s designs of childrenswear. After conducting several tests, the results showed a significant color-changing effect depending on temperature, the color fastness properties to light, wash, and rubbing were excellent. Antibacterial activity of printed fabrics was very good against Bacillus cereus and Escherichia coli bacteria and the anti-ultraviolet protection was found to be very good. The printed fabrics can be as protective childrenswear as shown in this work.