20 m old seems frightened outdoors

[shelbel]

ds is nearly 20 months. Up until now we've had battles to get him in his buggy as he's wanted to walk everwhere. Now if we're outside he soon wants carrying and it seems to be triggered when he points to the sky and sees a plane or the clouds - its as though he's frightened by it and even if he does walk he wants to be holding my hand which is a real difference from a couple of weeks ago. It started when i took him to a really big playground which i think he found overwhelming but now its whenever we're out. He also seems worried by other things outdoors like cobwebs or mud on the floor and again gets quite clingy. Has anyone any similar experience - is it linked to separation anxiety? Advice please.