Reunion (Side Quest)
Be careful around this one- unlike most quests it triggers automatically when you get anywhere near it, and you'll lose access to Senu until you've completed at least the first objective. Luckily there's no fighting until several more objectives have been fulfilled, but wandering through Herakleion Nome without your hawkvision can be a bit unnerving for lower-level Bayeks.
When you do enter the area, Senu is suddenly called away by another whistle, and does not return to you. Follow your marker to track her down.
This leads you to another of Bayek's old friends.
Follow her through the swamp, and to the pinnacle of some crocodile-infested ruins.
Noting that the ruins aren't as crocodile-infested as they ought to be, Tahira asks you to meet her in a nearby village. Before you go, you'll want to claim the fast travel point atop the Sobek statue.
When you hit the water, turn around to find a tunnel and treasure beneath the statue.
Meet Tahira in the hunting village of Natho. Senu can pinpoint the missing Child of Sobek, and other points of interest.
The place its being held is the Carcer Roman Compound
The Romans within are probably fighting the Child, so wade in when ready, either preparing the way with sniper fire or a backstabs (with a possible side of chain assassination).
Prioritize the camp leader, but kill all of them. When the compound is clear, loot the red chest at the base of the central tree to complete the location.
Now you have escort the Child home. It's an unkillable behemoth, so it's not the worst escort mission ever. Just stick real close, to keep it moving in the right direction.
You'll have to do some swimming and some fighting en route- just muscle on through. Don't forget Tahira, if you need a flanker, or a decoy.
Escort it all the way back home for mission completion.