My son has issues with constipation and has had since he was a baby. My tips are:

- as much water as possible
- prunes if you can get them to eat them
- prune juice (about 10ml to 100ml water and increase as needed). The best is if you boil some prunes in a small amount of water and then use that water dilated. Otherwise use the juice from the supermarket
- pears (tinned or fresh)
- licorice (best brand you can buy) if bubs will eat it
- if all else fails, then get a gentle laxative from the chemist (my son preferred Coloxyl)

HTH and good luck.