depends on how long the help will take, and what mess the other will create while waiting.

when #2 was a young baby, he was easier to get to sleep, so he got first priority and then i could focus on #1 to help her to sleep. However, if #1 was on the edge about to drop, then i would settle her first.

Toilet training was another tricky time. If #1 was rushing to toilet, or indicating she needed to go, then as long as #2 was safe he got left while i helped out #1.

Now #2 is toilet training, he gets priority (because i don't want to clean any more mess than i have to).

I hated it at the start realising that i couldn't commit myself completely to one child anymore.