Be a sympathetic listener without jumping to conclusions. Young children often begin the new year missing last year's teacher. Older kids need to discover that there are multiple ways of doing things. Try to help them recall other occasions when change ended up as a good thing. Young students may lose some of their enthusiasm when they discover they can't learn to read or compute instantly.
Older children fear they have forgotten everything from last year.
Keep your children's enthusiasm alive. Play games in which they use math to keep score. Try word games to build spelling skills. Do crafts or cooking to reinforce reading and fine motor skills. Whether they have just moved to a new school or started a new grade without old friends, the opening weeks of school can be lonely.