Are there negative developmental effects?
Assuming that childcare has any effect at all (e.g. more socialization, more familiarity with strangers), that same effect could be described as "negative" (e.g. less dependent on or 'close' to parents): so, whether any given effect is "negative" might be a (hard to quantify) subjective / value judgement.
I expect it also depends on the type of daycare. For example, putting a toddler into an overcrowded warehouse to watch TV isn't the same as putting them into a daycare environment that's richer in various ways (with better teachers, curriculum, socializing activities, teaching materials, etc.): so IMO the question is too broad to be meaningful ... the answer is, "well it depends on which daycare."
You're talking about daycare's "opportunity cost": that by going to daycare children forego the opportunity to spend formative years with their parent[s]. And that depends on whether the parents are available (on whether they're working); and also, partly, on how rich the experience of spending time with them is (whether they're interested, available, educated, educating, etc.): so, the answer is also "well it also depends on which parents."
conservatives advocating incentives for mothers to stay at home and progressives advocating for improving early childcare
That sounds like it might be a political question (not just an educational/developmental question): e.g. motivated by the perceived role of (private) home and family versus (public) state.
suppose that the parents and the childcare educators are both just as qualified in terms of education
The childcare educators might have two or three years of specifically ECE college training (developmental psychology, curriculum planning, etc.); and, 5 to 20 years of teaching experience, of teaching 10 or 20 children each year.
I'm not saying that parents would be less qualified, but their qualifications are normally different (unless they're trained and experienced daycare teachers themselves, which most people aren't).
'At home' and 'at daycare' are also different environments: the daycare has a peer group of 10 or 20 other children in the class (so there's socialization), likely a different time-table, and a different set of physical resources (I'm thinking of having and understanding e.g. the "Montessori materials").
I don't think it's sensible or possible to try to narrow the question by assuming that parents and teachers are "just as qualified" (i.e. that their 'qualifications' are equivalent).
Is it then problematic that the child in a childcare center has not a single reference person, i.e. today it's Alice, tomorrow it's Bob etc.? This was argued by the conservative part.
My experience with daycares is that there are two or three more or less constant teachers per classroom. There may be some small variation, for example:
- One extra teacher for half the day every day, if there are more children in the classroom for one half of the day (e.g. because some children do half-day kindergarten and half-day daycare)
- An occasional substitute teacher if a principal teacher is temporarily ill (or, for a longer period, on maternity leave)
- An occasional special-subject teacher (e.g. a visiting musician once a week, or a visit to the local municipal library, for the librarian to read a story)
A child is likely then to be with the same two or three teachers for the whole year (and maybe for more than one year in succession).
I'm talking about where the teachers have permanent (and more or less full-time) jobs, and the child is enrolled for every day for the whole year: the child would have a class, and that class would have a regular set of teachers.
I don't know of a situation where there's "not a single reference person": IMO there are usually reference people (children and teachers get to know each other within the first week or so), and if there are several reference people (almost always at least two adults per class simultaneously: not 'on successive days', but at the same time) then that's not a bad thing either (people don't usually have political objections to there being more than one parent, for example).
There is (so I'm told) some bonding (trust, knowledge, affection) which develop between the (regular) teacher and the child (to call the existence of such a relationship "negative" would be, IMO, unfortunate, but that's my political opinion).