Alice Cleaver simply got separated from her employers, the Allisons, in all the Titanic turmoil. She somehow got Baby Trevor away and they both ended up in a lifeboat. We can never know what confused conversations went on between the Allisons and Alice while they were all still in the cabins. But it is likely that Alice interpreted whatever she heard as an "instruction" to take Trevor to a lifeboat. Unfortunately, this was not the understanding of Mr and Mrs Allison. They simply didn't know what happened to Alice or Trevor and they stayed onboard the sinking Titanic searching for their "missing" baby. I do wonder why Alice Cleaver did not also have charge of the other child, two-year-old Lorraine. If she had, little Lorraine would have survived, and probably Mrs Allison, as well.