In Middle English, a 'ladde' was a youth or servant. 'Lad' can be traced back no further than that.
'Lar' in Latin was a household god. It can also mean a hobgoblin or a gibbon!
in liverpool and ireland, lar or lah is used as a form of address, such as 'alright la', and is also put on the end of sentences in the same way as 'man' might be.
it is just a shortened form of lad, same as ma and da for mam and dad.