Both of these are great for building the tongue strength!
Practice making the /s/ sound in the mirror after he brushes his teeth… 10x (keeping the snake in the cage… )
Practice the singular word and the plural with the board games (bat/bats)…. The /t/ is the same placement as the /s/…. By pairing these 2 sounds together, it helps the child produce the /s/ successfully! If you need… you may want to practice this with him in front of a mirror…. Dad…. purposefully make an error… let him know that you may mess up, and see if he can catch you!