I am no expert, but let them try.
Do you also offer eggfood, (presoaked) pellets and vegies? Those are probably easier on a young beak.
I'm no expert on weaning... but here is a thread from a true expert. I'm not sure if you are a somewhat experienced breeder, or if you purchased the chicks, or what, but I hope some of this information may help, until one of our experts comes along to give some personalized input.
[Thanks to SilverSage]
http://www.parrotforums.com/breeding-raising-parrots/74363-so-you-bought-unweaned-baby.html
Are you hand-raising/hand-feeding them, or are they being parent-raised? At 5 weeks yes, you can allow them to eat seeds...A great way to start the weaning process is to simply put a millet-spray either inside the nest-box if they're being parent-raised, or inside the Brooder if you're hand-raising them. That's typically how I start abundance-weaning all of the babies, by keeping a millet spray inside the Brooder, and once they get to the point where they are finishing the millet sprays, then I'll put a dish of pellets in, and stop the millet sprays/seeds. You definitely want them to wean onto pellets, so it's extremely important that after you're sure that they are able to eat/shell seeds, that you start keeping a dish of pellets in with them all the time, as they already know how to eat seeds and will willingly do-so, but not pellets. So i'd choose a healthy, NATURAL brand of pellets now, and be ready to start putting in a dish of them as soon as you're sure that they are eating the seeds (do not wean them onto any "fruit-flavored" pellets, as they are loaded with sugar, and if you do that they will never make the transition over to a healthy, Natural pellet).
The way I do it is first by confirming they can shell and eat seeds, then stop giving them any seeds and put in a dish of pellets each morning, and watch to see if they're trying them. If it looks like they are trying to eat them but having issues, then you want to soften the pellets a bit by quickly soaking them in a bit of water or fruit juice to entice them, and then once they are eating the softened pellets, slowly take away the water until they are eating fully-dry pellets. Keep a dish of natural pellets in with them all the time, and in the afternoon put in a dish of fresh veggies that are chopped into small, fine pieces that are easy for them to eat. Do the same with fruit as well. What you'll find is by doing this, the amount of formula you are feeding them in each feeding, and the number of feedings throughout the day will gradually decrease AT THE PACE SET BY THE BABIES, NOT YOU! Allow them to make the decision to eliminate a hand-feeding, or to lower the amount of formula in a feeding, which will happen naturally due to their crops being partially full from the pellets/veggies...If you're not hand-feeding them but rather the parents are feeding them, then they will handle that part, they know how to abundance-wean their babies and not "force-wean" them...
Green Cheeks usually fully abundance-wean between the age of 8 weeks old at the earliest, and around 12-13 weeks at the latest. So 5-6 weeks old is right on-track as far as them starting to eat solid foods.