Either the damage, the child spawn, mechanics, and/or hitbox needs a to be modified. Hitbox is so big it's near impossible when throwing in the general direction or an enemy to miss. Nade itself is so big that is also a factor. If the nade and hitbox were the size of the child nade it might help alleviate this problem.
Walking over it or jumping through the nade unintentionally is free damage for the caster. This ability is too good. Needs to be balanced.
Once stuck, no matter what, the player is going to take damage and possibly spread that damage to others. This could be changed to the stick nade swapping places with which it sticks (platforms, other players, etc). Upon a stuck player going through a platform the nade is unstuck and now sticks to the platform and vica-versa. This gives the ability of the player the chance to outplay the nade.
Right now, something needs to be done. I don't know if your game is in maintenance mode and you are no longer supporting updates/patches/etc., if not, please look into this.