I've never rinsed lentils in my life! Didn't know you were supposed to lol! And i've used them for soups, curries, and to make veggie-burgery things......never had any problems after it :/ but then i've never gave it to an 8 month old so i've no idea sorry!
I would think that boiling for a while would make sure everything was mushed down and any bacteria were killed though.....