The second set has to do with more philosophical matters: What is the purpose of nursery care? How does it fit into the rest of Sunday morning activities, such as worship and Christian education? What about Junior Church or having Sunday School and worship at the same time? And so on.
Let me deal with the second set of questions. Others are free to disagree with me, but this is where I'm coming from.
I am uncomfortable with having Sunday School and worship at the same time. That assumes that worship is an adult activity and Christian education is a child activity, which further assumes that worship is not something children need and Christian education is not something adults need (both false, I think). Worship includes taking part in prayer with the rest of the congregation, it includes being baptized and taking communion, it includes learning the songs and creeds of the Church. How can we say children have no need of this? And while many adult Sunday School classes may be pretty light on content, still, we have lots of adults who need to learn the doctrines of the Church, the content of the Bible, or be part of a regular meeting of spiritual companions. Even if people opt out of one or the other, to schedule them at the same time cheats anyone who wants both of something essential. The only way around this is in a charge with sufficient size to have two morning worship services, in which case one can still get both opportunities.
I have pastored a couple of churches who did Junior Church. The children usually left after my children's lesson to go to their activities in another part of the building. Many of these Junior Church activities were of questionable value; mostly, it was religious-themed entertainment. It made the parents happy because they were no longer distracted by their own kids; it made other adults happy because they were no longer distracted by kids belonging to someone else. The children, by and large, enjoyed their time out of the sanctuary (however spent), but when it came time to leave Junior Church behind about age 11 or so, many had a hard time making the adjustment to being one of the Big Folks and staying in the sanctuary. They didn't view confirmation as a gateway to More and Better in the way of their experience of God, but as having something they liked taken away from them; it wasn't graduation, it was exile. Having spent several years doing Junior Church, they were now the Big Kids, which meant they were top of the status heap among the Junior Church crowd.
I prefer to have all ages in worship. If someone needs to leave to attend to something (bathroom breaks or crying jags), well, that's okay. At the same time, I try to include children in everything we do, which includes doing a children's lesson (addressed to them, not over their heads to the adults listening in), kneeling to offer communion to the young on their level, and even preaching shorter sermons that are easier to sit through than the ones I remember from my own childhood. (Adults don't generally complain about the shorter sermons, either, I've noticed.)
As far as Sunday School goes, I would like to see our Sunday School teaching the faith in an orderly and age-appropriate way. The fact is, of course, that a lot of Christian education is haphazard because it's being led by volunteers who are very busy, often not well organized, or who have no overall vision of what they should be doing in any given class. There's a lot of "teaching lessons" rather than "teaching children," if you get my drift. People keep coming up with exciting new things that are basically ways of filling time or sparing the teachers trouble and that's no way to hold people's attention or to equip them to do anything. The old canard that the three most wasted hours in existence are spent in the doctor's office, study hall, and Sunday school is true often enough to make this Christian educator wince. Still, I'd rather try to improve Sunday School than try to combine it with worship in some way, which would just make worship less effective.
Which leaves us with the practicalities of the first set of questions. Nursery care is for those too young to look after themselves, and only when they need it. The usual place for very young Christians is with the other Christians in the sanctuary, but we don't expect them to behave like adults and when they need a break we should provide it. If some little kids want to go to the nursery right away -- or some parents want to take them there each Sunday, that's great; if the parents want them with them in the sanctuary, that's great, too. Meanwhile, if the Nursery worker is willing to sing and pray with the children, that's wonderful; however, nursery care is for the comfort and safety of the children, it's not Junior Church. I'm happy to have a paid child care worker for the Nursery, but having volunteers is fine, too. It really comes down to what the parents who need nursery care for their children prefer.