I have done this on many occasions. I make my decisions on some of the following questions:
#1 is this for a grade? Or will it cost ME money if he misses the lesson?
^ Those are YES.
#2 are you able to do it without switching your schedule around too much?
^ this is a maybe.. depends on my schedule and if I can do it without to much stress.
#3 Is there a way my kid could do this on their own? Walk, bike, go early with a friend?
^I like my kids to think of other alternatives to me and dad.. and sometimes it does work out that they can go with a friend.
Generally, I will not volunteer, I let them try to work it out and wait to be asked. If I keep jumping in to help, they will keep relying on me to pick up his pieces when he drops the ball. And my X was constantly dropping the ball.