OP here. I should clarify that even though our nanny works PT this consists of 3 long days each week, to match my work schedule--I am off the other days. There is no way that sports, camps, or any other activities would serve as child care for our oldest when he's 5--DH and I are gone from 6:30 AM until, best case scenario, 5:15 or so. It would be difficult even to find a day care that would take our younger one for the hours we need and to pick everyone up on time (factoring in travel time to 2 different locations).
OP your first post stated that you could put your 2 yr old in daycare and elementary school child in extended care 3 days a week. From your post above, it sounds like you can't find a daycare with hours 6:30-5:30 so I'm not sure what you are contemplating. Either it is an option or it isn't.
In our area before care starts at 6:30 am. We can barely make it to the bus stop by 8:45 so we haven't done it but do know some families who do. Your kid's sleep patterns would be important if they need to be out of the house by 6:30 am.
For after school, most elementary schools in our area let out at 3:30. Our 1st grade son does 2 sports and 1 extracurricular activity a week after school (activities are at the school) that run until 4:30: or 4:45. He then goes to aftercare for about 30 minutes to an hour until we pick him up at 5:30. I wouldn't choose a nanny over sports and it would be hard to find a nanny for one hour a day.