There is no toothpaste that can prevent 100% tooth decay. The only way to reduce decay chances are proper brushing, and rinsing done after every meal especially after eating sticky foods such as candies, rice etc. More than a toothpaste, good brushing technique is more important so that every area of teeth is properly cleaned. If your child is not able to brush properly you can also try a battery operated toothbrush till he gets used to the correct brushing technique.

Please see a video on brushing technique on youtube . Most of the times kids dont brush properly . And after every meal ask the kid to gargle so that no food is lodged .