Try just one dog at time no one around so you got all there attention,use there favourite toy,make it exciting,start off small distance,only 3 goes a day,if you keep doing it and they don't bring back they think that's the game,praise them if they bring back,allways finish on a good on,my dogs 10 month and penny dropped,loves the ball now.even jumped retrived for me the other day . Got to make it exciting for them.