For many of you - you'll instantly recognise the piano scene taken from the Tom Hanks 1988 movie classic 'Big'.
It's the tale of 13 year old Josh Baskin who hates being little and is zapped into the body of a 35 year old man with the help of the mysterious Zoltar machine.
Well the film is now a stage musical - and this week it's been premiered in Plymouth.
JAY McGUINESS, Plays Josh Baskin
GARY WILMOT, Plays George MacMillan
JAY: "In the first week of rehearsal Helen said, 'I love what you're doing it's very, you're reaching to get on the right key but you're having a laugh but you're also woaah, because it is meant ot be difficult for them as well and she said keep it like that and I said I've got no other option."
GARY: "What I have taken out of it is if there are any teachers, music teachers or physical education teachers they should get together and kids to do this in a school because it's a great fun way of keeping fit and learning music as well."
Gary's hugely experienced in musical theatre but for Jay - who's taking on the Tom Hanks role - he's having to channel his experience as a singer in the band The Wanted and his fancy footwork as last year's winner of Strictly Come Dancing.
And it's fair to say Jay has, just like his character, been channelling his inner child and loved being in Plymouth.
Form an orderly queue ladies and gents wanting to take Jay to the aquarium - but you haven't long - the cast of Big are only here until Saturday!