There is (Almost) Always a Way
The Problem. --- I won't belabour the point that the question, as it is written, is essentially storybuilding rather than worldbuilding. Ash gave us the elevator pitch, JBH brought out the Tome of Explanation. I know you're not the querent, Kaia, but to succinctly hammer home the point: whenever we see "which of A, B, or C would people want", this always means that we're dealing with the wishes or desires of people. By definition this kind of question is and ought to be closed for being too story based.
As written, this question also dives straight into the heart of narrative necessity territory. In this case, the story needs for a particular school of magic to be chosen by the pregnant mom in order to exist as a story! Essentially, narrative necessity at its most fundamental means quite literally that any story (as story) needs certain things to happen, otherwise there is no story worth telling.
The problem of questions that focus on matters of plot, character choice or NN, such as this one, is simply that any school of magic will fit the bill and thus answer the question. This is obviously not a good fit for WB.SE!
BUT!
What's Actually Going on Here. --- This is actually a great concept, and, as you say if we could hammer this question into shape it would indeed be a great addition to our repository! In its essence, what's going on here is a kind of Lamarckian inheritance. This exists in my own world, in positive, negative, neutral, and medial aspects and could easily be applied to a child's later magical intuition whilst being fearfully and wonderfully knit in utero.
As a quick example (though would actually have answered another recent question): there is a curious branch of magic that concerns itself with the subtle magic of breast milk. Galactothaumery. Milkdwimmery. Whatever you want to call it, it is a well known fact of biology that little children, regardless of their race, require milk for sustenance. It's less well known that children fed the milk from a wetnurse of a race other than their own can receive certain benefits and / or malefits depending on the relative "cross pollination" if you will. Very much in the vein of the present question, choosy moms choose certain well vetted wetnurses from particular races and social & intellectual strata to supplement their little babies' diets. With very much the same desire in mind: to give their little ones every advantage they can afford.
How do we Fix This? --- Our task then is how to look at hereditary thaumolamarckism from the external perspective rather than the internal. From the rules of the world perspective rather than the individual choice perspective. Let's look at the query!
So, the querent already deleted the paragraph that focused on a specific magical school. That's a good first step, because we really want to focus on the broader concept --- the rules of the world --- rather than the narrow choice that a family might make.
Good worldbuilding queries have five distinctive parts.
1. Marquee Question. The first thing we have to do to make this question properly answerable is to remodel the type of question! No character choice allowed! We need to focus on a world foundation rule, a law of nature, how such fundamentals might interact with magical systems, cultures, social strata, etc. The marquee question should grab our attention, point us in a particular direction, and make this querent's world and question stand out among the rest. I would look for something clever like Raising the Dead During Pregnancy: Your Child's Future is In Your Hands!
2. Background or Description. I would argue that the querent's background piece is good as is. We just need to gain a good yet succinct understanding of the world we're working with. Here, we've got magic, science, technology, social structures, and educational systems in play. This means that the world itself is actually pretty well framed out. We should be able to help this querent with understanding how the laws of nature will get him where he wants to go.
3. Variables, Area of Focus. We don't get much to go on here. The querent says "Note : This world isn't fully polished, so the full list of magic schools isn't set in stone. You can assume the usuals are there : Necromancy, Enchantments, Elements-bending, etc." The utility of necromancy is highly debatable; all three of these are fairly broad and could be interpreted in numerous different ways.
In this section, we respondents really need to be corralled and focused on certain things. We need to know a little more about these magic schools, a little more about how magic works, a little more about how culture and society interact with it. I mean, necroomancy could be the up and coming area of focus & study if this culture views dead bodies as a viable and legal resource to be put to work! Someone has to work the looms and the presses of this burgeoning industrial revolution! And slaves, children, and poor people all need to be fed, cared for and / or paid for their work; whilst zombie weavers really don't.
This section would need to be the querent's area of greatest focus.
4. Tell us the Real Question! This is where the marquee question is properly developed. The querent should take the teaser question, align it with the information within the background and focus it through all the variables he wants us to focus on and then give us the big reveal. It doesn't have to be clever, but it should meet our expectations.
Obviously, it should not focus on the parents' choices, should not focus on entirely subjective requests like "what's the best" or "which would they want". It should focus on the rules of the world. Here we could be treated to a question of environmental concern: How might a school of necromancy address a local community's environmental concerns over the increase in necromantically inclined student enrollment within the context of the city's several mechanised weaving factories?
5. Querent Expectations. This section is often ignored, but a good querent will always lead us respondents where he wants to go. So, we need to be informed what he expects from a good answer: Special attention should be paid to bits falling off of the workers and the variety of putrid corpse liquors contaminating the cloth produced by a zombified necroworkforce; the acquisition of raw materials and the effects of exhumation on local water supplies; economic and social factors of loud and obnoxious corpse raising incantations coupled with the difficulty of herding hordes of newly exhumed liches, zombies, and feral skeletons.
