Relatives baby is very floppy and behind with development

[August21yellowbaby]

the baby is 12 months old. He can’t sit up unaided, no crawling/walking
he is extremely floppy to hold, doesn’t hold his weight up when sat on your hip, you have to hold his back up
parents don’t take him to health visitor, and say he is just lazy, but something doesn’t seem right
he is in his car seat a lot I don’t know if that could cause this
the floppiness is something I’ve never seen before, he has no strength in arms or legs or in his back
anyone experienced similar and baby turned out to be fine?

That's extremely worrying. If they don't get him seen I'd be calling social services.

I think that you are right to be concerned but if the parents are just dismissing this as being lazy I'm not sure there's a lot you can do.

Also, they could be seeking medical help and may just be reticent to tell people, you never know.

Oh dear, that doesn’t sound normal at all. Agree with @MuggleMe - if parents don’t seek appropriate medical care that’s medical neglect and is classed as child abuse. The idea that he’s just “lazy” seems a really weird one.