As usual, Jesus' disciples didn't easily allow anyone so close to their master. Many times in the gospel we read about people coming to Jesus but being pushed by His disciples with reasons of not wanting the teacher to be over bothered, thay always wanted to protect Him.

Jesus allowed the little children to go to Him because the kids are always innocent of the world, that's why He said that, how He wishes, that all those who go to God, could humble themselves like little children.