We all get thirsty and impatient from time to time. Those foals were clearly not ready to wait for their mothers to move to a better spot.
Herdís climbs up on a bump to get a sip
Then we have this prankster from Gríma. He first tried to get his mother to stand up:
she was not ready to do that yet, so he just had some self service while she took a nap !