Exodus 17:3

But the people were athirst for water, and the people murmured against Mosheh, and said, Why hast thou made us come up out of Mizraim, to kill us, and our children, and our cattle with thirst ?

TO PUT US AND OUR CHILDREN AND OUR CATTLE TO DEATH WITH THIRST. In their complaint, they mentioned the cattle too, thus telling Moses that they need a lot of water and it is therefore necessary to take counsel on the whole matter. This is why it says at the second time [when the incident at the waters of Meribah is recorded], and water came forth abundantly, and the congregation drank, and their cattle., 20:11. Now here it is not mentioned but it is self-understood that when the rock was turned into a pool of water, they drank and they watered their flocks (Ramban in Verse 5 further). In the instance of the waters of Meribah at Kadesh, it is mentioned on account of the mishap that resulted from the entire affair, as explained there; see also Ramban here in Verse 5 for another interpretation. And our Rabbis have said: “They made their cattle equal in importance to themselves. They said: ‘A man’s beast is as his life. If a man travels on the road and his beast is not with him, he suffers.’”
Now the reason they mentioned us and our children and did not say generally: “to put us to death with thirst” or “to put to death this whole assembly,” [an expression] which would have included men, women and the little ones, as they said in other places,. is that by mentioning the children to him, they emphasized their murmuring against him so that he should make haste in the matter, since the young ones could not suffer thirst at all and they would thus die before the eyes of their parents. This is something like the expression, The tongue of the sucking child cleaveth to the roof of his mouth for thirst.