Sing ascending and descending scales using different words on a regular basis. Have children indicate ascent and descent using hands. Start on different notes. Play pitch discrimination game. Pupils close eyes while you play two notes fairly far apart on glockenspiel or keyboard.
Pupils indicate with hands if p or down.
Gradually get notes closer together. Make tongue and jaws work. Do not accept lazy singing. Sing on a regular basis and enjoy it. Play many notes while pupils indicate pitch with hands.