What means?
Hypotonia is muscle weakness or known as muscle tone. It can be a condition on its own, called begin congenital hypotonia, or it can be indeactive of another problem where there progressive los of muscle tone, such as muscular dystrophy or celebral palsy.
Symptoms?
Decreased muscle tone, muscles feel soft and doghy.
Ability to extend limb beyond its normal limit.
Failure to acquire motor related developmental milestones (such as holding head up ),
without support and walking.
Cause?
Unknown but these few disorders it can link to sometimes:
Down sydrome, muscular dystrophy, cerebral palsy, marfan syndrome etc.
Treatment
Physical therapy, medications
If you are adult and want to know about this condition more, i will suggest to write adult i just wrote the condition name and i found out later its children pages and i rarely use Wikipedia, because it's all fake there usually.