I wouldn't generally move for a 15% pay hike either. However, if it allow OP to take the next step up the career ladder (whether in terms of better status/brand name, more skills, better title, progression), then it is good for OP to build up some gas in her tank before dcs start to slow her down (temporarily but the pay/career hit extrapolates over those years) so better to start more senior.
The irony is that it is often easier to ask for flexible working when senior with specialised skills than junior.
With long-ish hours, the ability to be able to work flexibly is the key, whether it being allowed to move pt, flex the hours to start early/leave early (good for nursery rn as it avoids rush hour commute and allows drop off/pick up shift with dh), or working from home (bliss, no commute but still need childcare).
Risk should by nature be more flexible than other types of roles. I work in risk but in a different sector. I work from home practically 3 days a weeks now but pretty senior. It depends on the appetite that CS has for flex working.
OP, you don't have dcs yet but if you do take the role, it is worth keeping your ear to the ground on this. The more the managers like you, the more likely your flex working application will be facilitated (within the confines of the flex working regulations, of course).