Garden Wall Spaces Require Filling

[IMC]

Hi , Recently moved into a new house that has a boundary wall around one side of the garden. It has been built with a number of 1cm vertical gaps every 6-8ft. On the other side is a pavement and I would like to fill these gaps so that people (local kids) can't peer through the gap. I've noticed that all other similar walls in the area have a kind of putty looking material that fills these gaps. I'm assuming they are there for safety or movement and the builders forgot to fill them in? What do I use to fill these gaps?
Many Thanks

[The Builder]

.....they're for expansion/movement.....................use general purpose silicone sealant................chose your colour.... :o)))