HOW DO YOU MAKE THEM STOP GROWING!!!

JAX IS JUST GETTING SO BIG. HE LOVES HIS SWING AND WILL SIT IN IT FOR HOURS. I DONT LIKE TO MESS WITH HIM WHEN HE IS HAPPY,BUT SOMETIMES I JUST CANT HELP MYSELF AND HAVE TO PICK HIM UP:)! I BOUGHT HIM A PLAY MAT THE OTHER DAY AND HE LIKES IT AS LONG AS HE IS ON HIS BACK. HE DOES NOT LIKE HIS TUMMY AT ALL, SO WE HAVE BEEN WORKING ON THAT. HE DOES NOTICE ALL THE LITTLE FISHIES AND THINGS ON IT AND WILL JUST LAY AND STARE AT THEM! I WISH THERE WAS SOME WAY I COULD STOP HIM FROM GROWING SO FAST!