After caucus meetings the new MPs were officially welcomed to Parliament by Speaker David Carter to begin a two-week induction course.
Mr Mitchell said he was humbled and proud to be in Parliament.
Mr Muller said it was very much like the first day of school.
"The atmosphere has been great, we were given quite a special welcome and we gave an introduction about ourselves ... It does feel like the first day of school."
For returning Tauranga MP Simon Bridges, it was less like the first day of school, but still a humbling experience.
He said he was trying to help out some of the new MPs from around the central North Island.
"It's been great. There's a couple of things going on.
"For a lot of the new MPs this has been a moment to savour and they will never have this experience again."
He said there was a sense among returning MPs that a lot of trust had been placed in them.
"We really need to knuckle down and work hard."
Mr Bridges said MPs would find out in coming weeks what their portfolios would be.
The induction programme for new MPs would run over the next two weeks and would involve presentations from experienced MPs, role-playing to familiarise them with Question Time and select committees, and how to avoid embarrassing headlines over improper expenditure or hiring family members.