My baby boy's weight is a concern please advise. It's 9.65kg. 21 months

Please read this article
Height And Weight Chart: An Easy Tool to Monitor Your Child’s Health

Baby Weight Gain: What Helps And How

if a baby is really active, interactive coping up well with milestones and development, then do not stress much on the weight but of course you can always feed laddoos or food added with dry fruit powder to build up weight. Always ensure a well balanced nutritious diet.