Besides the mashed veggies you can also soften your choice of pellets with water and start to offer them. They'll probably just play with most foods at this point, but it's important to get them exposed to different foods asap. In general they wean around 10-12 weeks, but every bird is different so just watch and be sure they're eating on their own and not losing weight. Weigh them everyday to be sure their gaining, and if not keep supplementing with hand-feedings.