The English to-infinitive structure has over a dozen different functions, presenting a difficult area for EFL students. The present study shows a relatively dynamic profile of the use of ten to-infinitives functions appearing in EFL children's story writing as the children progress in grade levels and English proficiency—an area that has never been investigated previously. To-infinitives that function as an ‘object’ or ‘purpose’ were most prominent. The students used a higher number of to-infinitives as they progressed from the third to sixth grades. The increase between the four adjacent grade levels did not reach a level of significance, but the increase between middle (third and fourth) and upper (fifth and sixth) levels was significant. The difference was striking when the entire group was re-sorted into lower vs. higher proficiency groups: the increase in the use of to-infinitives was better explained by English proficiency improvement than by grade level progression. This in-depth analysis into the sub-functions adds to the existing knowledge about to-infinitives, which might otherwise remain oversimplified.