Take your time. Go nice and slow.
Repeat parts that are difficult. Don't always start at the beginning. Once you've worked out trouble spots, play the fixed part with the rest of the song.
If you're using the video for help, don't forget that you can pause it or slow it down.
Hot Cross Buns Practice Video
Gently Sleep Practice Video
Au Clair de la Lune Practice Video
Mary Had a Little Lamb Practice Video
Boat Song Practice Video
Twinkle Twinkle Little Star Practice Video
Old MacDonald Practice Video
Peace Like a River Practice Video
Down in the Valley Practice Video
Ode to Joy Practice Video
Jingle Bells Practice Video
D E F# G A
D E G A B D'
When the Saints Go Marching In