Deb is right about not giving them too much in the way of treats. They're growing at a tremendous rate and they need the complete nutrition of their starter/grower.
Like little human peeps, if you give them a choice of junk food or a healthy meal, they'll go for the junk food every time. Not that treats are junk food, but you get the idea.
I feel it's best to start with the simplest foods first. Try some chopped hard boiled egg or some plain, low fat yogurt. Both are good for them and will get them used to trying new foods.
After that, add new treats one at a time. Wait a few days and add another, always in reasonable amounts.