was this grandmother or mom out of line?

Ok i feel both were a little but who was more. Yesterday i went to Hollywood studios in Orlando Florida. we are annual pass holders. They used to have a parade now its called the block party that is nor here nor there but we were sitting over a hour before the event to have good seats. this older lady in her 60s to 70s comes up with a little boy about 4 to 5 years of age. it was very hot out and he didn't want to see a show that was going on in the park. so the grandmother excused her self from the show and opt to sit next to my family and myself. upon the lady sitting with her grand son for about 25 min she said she was getting thirsty and needed a cold beverage. but she really didnt want to loose her spot. so she asked if i didnt mind to look after her grand son as she walked 40 ft to the drink cart. i told her not a problem and its not like you cant see him from where you will be so between me and the little boy we ward off all the people wanting to take seats. but while the grandmother was walking back her daughter and rest of the family came to the location. and said where is my mom i proceeded to say she is getting some drinks and said oh wow my mom trusts everyone and leaves my kid with strangers. i was in a way taken back here there family were able to run around and have really good seats and yet yelled at her poor mom for being thirsty and getting a drink yet still maintained the seats.

who do you think was in the wrong?