... is not a phrase the girls are familiar with... yet. But I think L'il Sis already understands the gist.
Yesterday, the girls were rough-housing and somehow ended up in my room. Big Sis banged her knee against my bed's footboard. There was much wailing and moaning. We checked and her knee was fine aside from a red spot, but that could have been from her rubbing it as well. At any rate, Big Sis was on the bed, holding her knee and crying, "It hurts! It hurts!"
L'il Sis, being the sweet little sister that she is, kept bringing things to Big Sis to help her feel better. First, it was a paper cup with a sip of water. This was followed by a bandage (no blood so not really needed) and then her sleep mask so that Big Sis wouldn't have to look at her boo-boo (again, it was just a little red spot).
Eventually, L'il Sis brought in a little pink egg-timer that their dentist had given them and said, "When the sand runs out, you have to stop crying."
Big Sis responded with, "But that's only 2 minutes!"
If L'il Sis had known the phrase, I'm sure she would have used it: Suck it up, buttercup!