I never recommend baby bouncers.( paediatric physiotherapist for 30 yrs and a mum)
When a child is able to move from horizontal to vertical
itself would be the first time you are probably not doing any harm. I have never read any studies about baby bouncers. The most important people, who really know a lot about developmental neurology, are the ones to "ask". I suggest you start looking up(google of pubmed) prof. mijna hadders-algra´s work. She is a specialist in the development of truck and posture. if you can learn a little more about the natural development you might even throw the whole thing away.
When a child is as young as your child is, it still needs a amount of trunk support when being held vertical. Most children who have started to "standup" at such an early age are "standing on their reflexes". From 3-4 months(corrected) age reflex activity slowly changes into goal related movements.
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dear junior physiotherapist, if you want ot know what a babybouncer is go to
www.youtube.com and type baby bouncers and you will find various films featuring babies in these bouncers.
regards
esther