Just finished a three hour game session with the kids.
They are uncertain about a dungeon where you walk 200-400ft between dungeon rooms. (Entire main hallway is 1 1/2 miles long and exits into a volcano they are not aware of (evil DM

)
The Living Spell of Burning Hands was no problem
The 4 Fiendish Medium sized Dire Snikes were an issue for summoned nature's allies only.
However... the medium water elemental in a pool of water was not very popular with my son. After 5 rounds he was down to 1 hp and 1/2 drowned. In the end, we got him out of the water and fled the pool hoping it was restricted to the water.
The next room should scare them a bit. Crypts filled with swarms, zombies and a few Mad Slashers just for the fun of it. (Evil DM

)
I'm sure the later room with the dead 1/2 dragon storm giant will really give them a scare. (Very Evil DM

)
Anyway.... that'll be tomorrow.
along with the duegar, traps and eventually the warforged of House Cannith. And before I forget... a lava bed to traverse carefully.