My Lavender bush has white little bubbles on it

Its the protective froth created by froghopper lavae. The froth is harmless to the plant , as is the creature itself although the lavae does suck a bit of sap, but it is very tiny.
You can wipe the froth off by hand if you dont like it or give it a good rinse from the hosepipe - sometimes it gets called 'cuckoo spit'

in a nut shell ducky.:o) the critter is quite fun to look at close especially if you have kiddies.