"If you are sure the cellulitis is preseptal, there is no proptosis and the eye looks reasonably good behind the lid and as you say, the child seems to be a little better, I would not think it necessary to drain the upper lid. Unless you feel and see a discrete pustule, the incision, and that tissue I see on the lid may be one, you will most likely just cut into tissue that seeps but does not yield the "gush" of puss you might hope to see come out.
On the other hand, a small incision parallel to the lid margin a few mm above the lash line over the top of a pustule would probably not be of any harm regarding a scar, but in the condition you describe, I do not think a lid incision would help this child.
Of course, post septal cellulitis is another and more serious story.
Have you done imaging? It is probably not necessary.
You could try warm soaks. It looks like you are doing the right thing.
Let me know how this turns out."
The partner responded the next day saying that the upper lid swelling drained spontaneously and that the patient continues to improve.