Li Shenron
Legend
I have finally started playing D&D 5e with my children. Talking about breeding your own gaming group as the only way to have a stable one these days 
Anyway, after a one-shot introductory adventure (conversion of "A dark and stormy knight" from 3e), in the second session we started a longer adventure (conversion of "Horror on the hill" from BD&D), the final encounter of which can be a young red dragon!
So I am trying to make some considerations in advance related to the dragon. I want them to find it, because after they finished their first adventure my children immediately asked "so this was the dungeon, but where is the dragon?"
Naturally I'll have to use the weakest option i.e. Wyrmling, which is anyway going to be very tough on its own: it's CR 4 and 1100XP, so assuming they'll be 3rd level when they get there, it's already (albeit barely) a "Hard" encounter according to the DMG.
One thing that isn't clear yet, is whether a dragon this young should be using lair actions. I don't know for sure if a wyrmling doesn't have lair actions at all, can have lair actions (but they aren't included in the CR and XP, which should be increased) or should have lair actions (included in the CR and XP).
I am confused by some mildly conflicting information here:
(a) lair actions are not written inside the stat block but instead presented in the "A dragon's lair" section for each dragon type, so they look like they apply to all dragons of such type
(b) regional effects in the same section explicitly mentions legendary creatures, while lair actions don't
(c) the MM introduction mentions lair actions only in the context of legendary creatures, and only Adult and Ancient dragons have legendary actions
(d) someone pointed out that there are monsters with lair actions but not legendary actions (although I couldn't quickly find an example in the MM)
So (a) and (b) seem to suggest all dragons have lair actions but (c) suggests only the legendary ones. Maybe there was a Sage Advice to clarify?
Using lair actions would be very cool, but I wouldn't want to make the encounter even harder, so if it's not counted into the current CR/XP, I'll skip it. Or maybe I'll just use the "drop prone" effect, but not the lava damage which sounds quite high for CR 4 to me.

Anyway, after a one-shot introductory adventure (conversion of "A dark and stormy knight" from 3e), in the second session we started a longer adventure (conversion of "Horror on the hill" from BD&D), the final encounter of which can be a young red dragon!
So I am trying to make some considerations in advance related to the dragon. I want them to find it, because after they finished their first adventure my children immediately asked "so this was the dungeon, but where is the dragon?"

One thing that isn't clear yet, is whether a dragon this young should be using lair actions. I don't know for sure if a wyrmling doesn't have lair actions at all, can have lair actions (but they aren't included in the CR and XP, which should be increased) or should have lair actions (included in the CR and XP).
I am confused by some mildly conflicting information here:
(a) lair actions are not written inside the stat block but instead presented in the "A dragon's lair" section for each dragon type, so they look like they apply to all dragons of such type
(b) regional effects in the same section explicitly mentions legendary creatures, while lair actions don't
(c) the MM introduction mentions lair actions only in the context of legendary creatures, and only Adult and Ancient dragons have legendary actions
(d) someone pointed out that there are monsters with lair actions but not legendary actions (although I couldn't quickly find an example in the MM)
So (a) and (b) seem to suggest all dragons have lair actions but (c) suggests only the legendary ones. Maybe there was a Sage Advice to clarify?
Using lair actions would be very cool, but I wouldn't want to make the encounter even harder, so if it's not counted into the current CR/XP, I'll skip it. Or maybe I'll just use the "drop prone" effect, but not the lava damage which sounds quite high for CR 4 to me.