dont know if this has been mentioned before so apologies if it has
but as most of you know I have a ds2 who cant walk but I found a company that makes trikes for kids with sn.
we got ds one for xmas last year and even though his body tone can be either stiff or floppy, he can still ride this. He is like a 6-9 month old.They have a parent handle that can brake etc and are safe.
They are expensive but you can get funding from charities. I did.
Take a look at this