The Bible does not teach that children have “guardian angels.”
Reading in context the passages Matthew 18:1-14 and Mark 9:33-46 we discern that Jesus, on both occasions was alone with his disciples, no children were present. Jesus said to them:
The bald inserts in brackets in the verses are mine.
The Parable of the Lost Sheep.
Matthew 18:10-13 (NRSV)
10 “Take care that you [apostles] do not despise [by what you
say or do] one of these little ones; [Jesus disciples] for, I
tell you, in heaven their angels continually see the face of my Father
Following that, to show the preciousness of the little ones, Jesus, told them the parable of the lost sheep.
12 “ What do you think? If a shepherd has a hundred sheep, and one of
them has gone astray, does he not leave the ninety-nine on the
mountains and go in search of the one that went astray? 13 And if he
finds it, truly I tell you, he rejoices over it more than over the
ninety-nine that never went astray.”
Mark also mentions the “little ones”. Mark 9:42(NRSV)
Temptations to Sin.
42 “If any of you [apostles] put a stumbling block [by what you
say or do] before one of these little ones [ Jesus disciples]
who believe in me,[a] it would be better for you if a great millstone
were hung around your neck and you were thrown into the sea.”
To stress the seriousness of the sin, a millstone an ass usually turned, hanged around a person’s neck and thrown into the sea, with this heavy weight a person would have no chance of surviving.
We have seen that the phrase “little ones” does not refer to children but to “Jesus disciples” the ones that believe in him. Therefore, Jesus did not mean that children or individuals have a guardian angel, but that angels show interest in his disciples.
Jesus also called his disciples “little flock”. Luke 12:32; “Do not be afraid, little flock, for it is your Father’s good pleasure to give you the kingdom.