Your child can benefit from learning sign language, even If they're not deaf or hard-of-hearing. Any child, who can communicate in both sign and spoken language has a bilingual advantage as sign language is classified as a world language, the same as Spanish, French, or any other foreign language. Therefore, if a child speaks sign language, the child is considered bilingual. 
Studies show long-term cognitive benefits, including:

• +12 IQ point advantage
• Accelerated speech and emotional development
• Effective communication
• Lower frustration levels
• Improved child-parent/care-giver bonding
• Reinforcement of learning of educational concepts such as ABC's, animals, etc.
• Improved word recollection in children because there is muscle memory involved, and the more senses involved in learning, the greater memory retention the child will have
• Improved attentiveness to social gestures of others as well as of themselves
• Larger speaking vocabulary and ability to form longer sentences
• Earlier reading and larger reading vocabulary
• Better grades in school.

*Source
Learning resources are scarce but here's where your child can learn Kenyan Sign Language (KSL) to compliment their curriculum
Kodomo Kids
A Youtube Channel dedicated to teaching Kenyan Kids life hacks MORE
Akili TV
Akili TV is known for it's wholesome child content and they have shows for deaf children or kids interested in learning KSL  MORE

*Featured Image: Akili Kids