If I leave the airport during layover what happens to my luggage?

Hi! We are flying back to the US this fall from Nairobi to Atlanta via London Heathrow. We 8-9 hour layover in London. I would really like to leave the airport during that time to catch a few of the sights for my kids who have never been there before. So my question is - can we check our luggage all the way through or will they somehow know if we leave the airport and that affect our bags. We will have between 10 and 12 bags plus 3 checked car seats and 1 checked stroller (we are moving home after being here for 2 years) so this is obviously a huge issue and we can't plan on going in if we have to claim our luggage. Left luggage would be a nightmare with that many bags (not to mention the cost). I was just hoping to get it figured out so I can plan! Thanks!