TLDR: baby pterosaurs – even hatchlings – had wings fully specialised for active flight, were also excellent gliders, but almost certainly had very different lifestyles and occupied very different niches from their parents.
For starters, it’s important to note that the idea that pterosaurs were able to fly very soon after (potentially immediately after) hatching is not at all new. This view has, in fact, been popular and well supported for a few decades now and has its strongest evidence in the fossils of very young juvenile pterosaurs, and even hatchlings still in their eggs. These have fully developed wings, adult-like proportions, and wing membranes similar in size and extent to those of their parents.
(...) Could it be that baby pterosaurs lived with their parents in the same way that, say, baby gulls or shorebirds do? As we say in the paper (Naish et al. 2021), this is by no means impossible or implausible.
(...) What appears more likely, however, is that parental care simply wasn’t needed and likely didn’t occur, the juveniles living an independent life in a totally different environment from that used by their parents.
Bennett proposed this for Pteranodon (Bennett 2018), arguing that juveniles inhabited inland environments, only later moving to oceanic habitats much later in life. We agree and go a bit further in arguing that this phenomenon – ontogenetic niche partitioning – was widespread and normal across pterosaurs. The fact that the wing proportions of juveniles allowed more dynamic flight and steeper climb abilities, coupled with their small overall size, could mean a reliance on more manoeuvrable prey and exploitation of cluttered, vegetated habitats unavailable to adults (Naish et al. 2021). In short, hatchlings and young juveniles likely occupied very different niches from older juveniles and especially from adults.
The picture that emerges here is one similar to that established for some dinosaurs. If the juveniles of big-bodied species were occupying distinct ecological niches from their parents, they were essentially functioning as ‘different species’. The result: one species functions as ‘several’ across its lifespan, is potentially better at exploiting niches and resources across its environment than would a species with a more conserved niche, and a low number of species (potentially even one) can occupy the niches used by several or many species in another animal group. You may already have heard of dinosaur-based studies that posit big theropods (specifically tyrannosaurids) as similar ‘niche fillers’, their juveniles apparently able to occupy ecological space ‘ordinarily’ used by species with smaller adult body sizes. Well, it might be that the same was true for pterosaurs too.
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