You might end up having to start them with something live if they don't catch on. Fish-wise guppies are a safe option. A less expensive route would be to get some lobworms to start them off - Fishing Worms and Bait - Lobworms | Worms Direct
These will wriggle about in a bowl of fish strips and will entice most to eat. You can then gradually reduce the amount of worm until they are on fish as the staple