My DS1 (4 yrs old) does have quite low muscle tone. I have had him at an OT a few times and they helped us to try new things with him. I think it is just something they will live with - but she helped me to help him to overcome some of it with him. I only had 3 sessions.
there were lots of ideas - and one of the best thing is she helped to me understand WHY some stuff is hatrder for him than it is for other kids. that has helped me alot.
she also had a special vest he can wear to train someof his core muscles and that helped in the sessions (i need to buy him one)
I would suggest you go to an OT for an assessment and see what they say - i found it v useful.
Feel free to PM me i fyou want to chat more about it.

PS no signs of it at all with DS2, who is 2.5