i have two chihuahuas.
my son boy has always been so careful around them, until he hit about 19 months.
recently he’s became so heavy handed with them! he isn’t a heavy handed child with anything else, nor aggressive/heavy handed with other children.
i know he’s young and he doesn’t intentionally mean to hurt them, but he does.
i’ve caught him pulling them around the front room by their tails, their back legs, he throws blankets over them, throws toys at them etc.
i give him a STERN telling off every single time, i get the bottom lip back. but an hour later he’s back at it. one of the dogs is petrified of him. and backs herself into a corner.
it’s to the point where i’m having to put the dogs in their dog room under the stairs or outside every single time i want to leave the room/go upstairs etc.
i know he’s not doing it to be horrible, and he doesn’t understand that what he is doing is wrong. i don’t want to see my little dogs hurt, nor do i want them to eventually snap in defense!
but how can i get him to stop quick. i feel so bad on my puppies ! 
Just to add, i try not to give the dogs loads of attention after, just incase jealousy was a factor… i do however show him to be gentle and how to stroke them. to which i say ‘look, gentle’ which he does!!! then 30 minutes later he’s back to before.
i’m trying to persevere but is there anything else i can try?!?! please ?!?!