animals are getting out of fenced areas

when i build my farm everything was fine. i started building animal farms then with fences going all the way around (no possible way out) i put multicoloured sheep in one pen, chickens in one and cows in the other. everything was going great as i expected. i went home went to sleep then my sister told me to go to the farm when i got there 2 sheep, 3 chickens and one cow got out somehow. some cows sheep and chickens was still in the fenced area. the dimentions of the 3 fenced areas was 8,8 each. i had 2 cows in one 5 sheep in the other and 8 chickens in the 3rd

i thought they would stay in the fenced area

they got out

1.make a fenced area with dimentions in 1st paragraph.
2.then get sheep, cows and chicken with wheet from out side (eggs for chicken) then sleep