I'm DMing a group of 6 rookie PCs in LMoP right now, and our second session was last night. Hoo boy, it was a bloodbath, and most of the group presumes they're dead now.
My group actually got up the chimney in the wolf room and got the drop on Klarg. Some good rolling led to most of the baddies dispatched in the surprise round. In fact, the rest of the cave went pretty smoothly after that.
When they got into town, though...
The group got the wagon to Barthen's, where he told them they looked tired and ought to check out the Stonehill Inn. As sort of an off-hand comment he added, "and stay away from the Sleeping Giant." (As the DM, I was fishing for some follow-up questions to introduce the Redbrands.) The group didn't ask any more questions, they just took their gold and left.
Once they got outside, the group made plans to go to the inn. The tiefling druid, dwarf druid, and human sorceror started making their way to Stonehill Inn. The half-orc barbarian talked the elf rogue and halfling ranger into going to the Sleeping Giant to look for trouble. At this point, nobody knew anything about the Redbrands.
(When I was preparing this stuff for 6 adventurers, I decided to up the "Redbrand Ruffians" encounter to 6 Redbrands. I also gave half of the Redbrands more varied weapons than just the standard shortswords. My expectation was that the group wouldn't split in half before the Redbrand encounter. With the way the story was moving, though, it seemed like the right call to keep the baddies as I'd prepared them and see what happened.)
Gorn, Valus, and Althreigh enter the Sleeping Giant, notice that there are six well-armed men wearing studded armor and grimey red cloaks. The halfling orders a round, and the barmaid backs away silently into a back room and locks the door. The three adventurers then notice that they're cornered by a half-circle of six Redbrands.
At the same time, Zeza, Agnetha, and Simon arrive at the Stonehill Inn. Simon is spent, so he buys a room and goes straight to bed. Zeza and Agnetha order some ale and start asking if anyone knows anything about Cragmaw Castle or Wave Echo Cave. The people they ask don't have much information about either, but they do lament that the trail isn't safe to travel, and no longer is their town safe either. This time the druids take the bait and ask what that means, learning about the Redbrands in the process. A few questions in, and they learn that the Redbrands are well-armed, tough, and running their in-town operations out of the Sleeping Giant. The druids realize that those three idiots just walked into way too big of a fight for them to handle.
Cut to: Gorn, Valus, and Althreigh in way too big of a fight for them to handle. Gorn's rolling poorly, but he still manages to greatsword a bad guy down to half his HP. One of the Redbrands (affectionately named Big Dum Dum) recently pillaged a morningstar, but he has no idea how to use it. (He rolls his attacks without proficiency, and spends most of the fight bumbling. He does have 22 HP, though) Valus was down to 8HP by the end of the goblin hideout and nobody's taken any rest, so he uses his disengage as a bonus action and dashes out the door. Althreigh draws two shortswords and goes all salad shooter on three guys at once.
Three rounds later, the druids running from the Stonehill Inn see the elf rogue leaving the Sleeping Giant at full-sprint. He waves them in and doesn't need to explain that there's trouble. The dwarf druid wolfs out and charges through the saloon door, biting a Redbrand in the face and knocking him prone. She then takes a warhammer to the head and gets knocked across the room. The half-orc barbarian and halfling ranger get knocked unconscious and they're bleeding out on the floor, it's the wolf that has the Redbrands' attention now. The elf ranger scatters 1,000 ballbearings on the floor and 2 Redbrands slip and fall. This distraction gives the tiefling druid enough time to drag the half-orc barbarian out of the fray, then to book it back to the inn to wake up the sorceror for backup. Not one Redbrand has fallen.
The druid rouses the sorceror and they run for the Sleeping Giant. They get there 3 turns later and find it completely deserted.
(My plan is for the 4 KO'ed adventurers to wake up in the prison under Tresendar Manor. Sildar's going to volunteer to help the sorceror and the druid track down where the Redbrands might have taken the prisoners)
TL;DR The six adventurers got into Phandalin, and three of them decided they wanted to go looking for a fight. Four of them got KO'ed by Redbrands before they even learned what Redbrands are. Instead of a near-TPK, they're locked up under Tresendar Manor now, the dummies.