i think its " Those canaan days " from the show Joseph and his Technicolor Dreamcoat , an instrumental version on piano by Lloyd Webber, thats as close as I can get !
Here's These Canaan Days as norton500 seems convinced that Chim Chim Cheree is wrong. AB charlie has a few options here- let us know whether you think any of these is the one you were thinking of
It's definitely 'Hushabye Mountain'...though people can be forgiven for also hearing 'Chim Chim Cheree' as the chord progressions are virtually the same for both songs, which were both written by the Sherman brothers. Since the theme of the ad is being sleepy, it only makes sense that they are using the well-known lullaby from the film Chitty Chitty Bang Bang.