Flexible hours negotiation - how much is too much to ask?

Currently working 8:30-5:30, want to propose 7am-4pm so I can pick up my kindergartner at 4:15. Earlier start sucks but the pickup would change everything for my family. My manager is pretty chill but I don't want to seem unreasonable. We're not a super flexible company culture but we're not corporate either. Is this a normal request or am I asking for a pony?