In order for people to understand what they are saying, children need to hear the sounds in words, remember them accurately and say then say them clearly and fluently.
Make sure children can see your face - it will help them know which sounds are in words
Keep the background noise as low as possible when you are talking to them. It will be really hard for them to hear the sounds clearly if there is lots of competing noise
Don't ask them to repeat a word unless you genuinely didn't understand. Repeating doesn't help - they are probably already giving you their best attempt.
Instead of asking them to repeat, try to use the word yourself so they have a really clear model of how the word sounds when a grown up says it
Clap new words out together. This will help them to really hear and remember all the sounds in the word