It is a common theory (even in-universe) that the Ghost of High Heart is actually one of the children of the forest.
From the linked wiki:
While most people believed the woods witch to be a dwarf, her friend, Jenny of Oldstones, claimed she was one of the children of the forest.
Which brings us to another point, Jenny of Oldstones was friends with this particular woods witch. Jenny was the wife of Duncan Targaryen, and while we don't know when she was born, we do know that the Prince of Dragonflies was born in the early 220s. Even if the witch was born around the same time, that would put her around 70-80 years old, which is very old for someone that lives alone in the wilderness(at least for a human).
There is plenty of evidence that this is the same woods witch that Jenny was friends with. The biggest and most obvious is that all she asks for her prophecies is some wine and a song: Jenny's Song. Most people believe that the Jenny in the song is the same Jenny of Oldstones. IIRC when Tom was singing it to her, there were tears streaming down her cheeks. Also she says this to Arya:
I gorged on grief at Summerhall, I need none of yours.
Summerhall being where Jenny and Duncan Targaryen died.
Then there's this line from Thoros that brings it all back around:
... she has her own ways of knowing things, that one. The weirwoods whisper in her ear when she sleeps.
Which matches how we've seen other children of the forest get their information about the past, the future, and distant events. All signs point to her being a lonely child of the forest.