You needn't be worried, a Druid and a Cleric can look after themselves in melee quite well. It's a question of mindset mostly. If those two are played as healers/party buffers, you'll lack melee staying power. But if you look at what the classes really can do, you'll see that they're very, very capable in melee, and still have other options (like full casting...) to fall back on.
An important question, however, is starting level: both Druids and Clerics can melee from level 1: One has an Animal Companion that's as good a fighter as a fighter, and the other has heavy armor and shield proficiency to stay alive.
But both become really, really good at melee from levels 5 and 7 onwards, respectively: the Druid learns Wildshape, and the Cleric gets Divine Power. Try to remember these important break points to utilize as yardsticks for planning out the campaign.