Sleep training

I've got 2 granddaughters aged 4 and 2 who I look after regularly. Last night I baby sat while their mum went to a hen do, their dad is away for work. Getting them to sleep was mayhem, they were screaming blue murder and calling for their mum, and they kept it up till their mum got home. I found it very upsetting, especially when the 4 year old was kicking me and screaming at me to go away. I felt useless and rejected. I know it's not just me, bedtime is difficult and takes ages for the parents too. Their mum is thinking about sleep training, does anyone have experience of this and maybe a recommendation?