Hello Heidi!
L3 and L4 both innervate knee extensors, so you would expect a degree of quadriceps weakness if these are affected. Clinically, the “level of weakness” varies from person to person because “lesion levels” do not all act the same. There are some institutes that do not even provide lesion levels because of how much variability is seen from patient to patient. I think the overall take away message for L3 and L4 lesions is that the child might have knee extensor weakness and you should then understand what secondary impairments could occur because of this weakness and what orthoses or assistive devices may be needed.
Does this help answer your question?
Jessica