We estimate the number $$|\mathcal {A}_{{\varvec{\lambda }}}|$$ of elements on a nonlinear family $$\mathcal {A}$$ of monic polynomials of $$\mathbb {F}_{q}[T]$$ of degree r having factorization pattern $${\varvec{\lambda }}:=1^{\lambda _1}2^{\lambda _2}\ldots r^{\lambda _r}$$. We show that $$|\mathcal {A}_{{\varvec{\lambda }}}|= \mathcal {T}({\varvec{\lambda }})\,q^{r-m}+\mathcal {O}(q^{r-m-{1}/{2}})$$, where $$\mathcal {T}({\varvec{\lambda }})$$ is the proportion of elements of the symmetric group of r elements with cycle pattern $${\varvec{\lambda }}$$ and m is the codimension of $$\mathcal {A}$$. We provide explicit upper bounds for the constants underlying the $$\mathcal {O}$$-notation in terms of $${\varvec{\lambda }}$$ and $$\mathcal {A}$$ with “good” behavior. We also apply these results to analyze the average-case complexity of the classical factorization algorithm restricted to $$\mathcal {A}$$, showing that it behaves as good as in the general case.