Congratulations are in order for J.J. Watt and his wife, Kealia ... as the former all-pro defensive end and soccer star announced the birth of their second child -- Niko!!
The three-time Defensive Player of the Year shared the news on social media Tuesday ... introducing the world to their newest bundle of joy with a series of sweet photos where everyone -- including their firstborn, Koa -- was nothing but smiles.
"Overcome with joy and gratitude," he wrote.
The comments on their joint post were flooded with people pumped over the news .