For those of you that didn't know or never realized it, when babies are young their arms are too short for them to be able to touch their hands above their head.
Either that or their heads are just too big.
The latter being the more probable explanation.
Babies need time to grow into those big fat heads.
Well Ronan has reached another milestone.
He is now able to stretch those arms and touch his hands above his head...
with Daddy's help.