我知道childrenCount对valueEventListener有一个功能，但是childEventListener是否有childAdded类似函数在Gib <- as.numeric(geocode("Gibraltar"))
overlay <- stat_density2d(aes(x = long, y = lat, fill = ..level.., alpha = ..level..), bins = 16, geom = "polygon", data = EATL_pts)
EATL_map <- get_map(location = Gib, zoom = 3, maptype= "satellite")
EATL_map <- ggmap(EATL_map)
方法之前对每个孩子进行计数？