What is the limit to joking for children with their parents in order that it not be offensive? Does Islam allow children to joke with their parents?

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger. 

It is allowed to joke with one's parents or others without lying, especially if it is needed to attain a benefit such as making them happy. This is evidenced by the hadeeth which was narrated on the authority of Ibn ‘Umar, may Allah be pleased with him, who related that the Prophet, sallallahu ‘alayhi wa sallam, said, “Indeed I joke, but I speak nothing but the truth.” [At-Tabaraani] He, sallallahu ‘alayhi wa sallam, also said, “The most beloved of deeds to Allah is to bring happiness to a fellow Muslim's heart.” [At-Tabaraani]

It should be noted that joking with parents requires extra politeness and respect given their status. If the children go beyond the limits of politeness and decency, it becomes prohibited because it would be considered undutifulness towards the parents, which Allah forbids; Allah, The Exalted, says (what means): {...say not to them (so much as), “uff,” and do not repel them but speak to them a noble word.} [Quran 17:23] Ibn Katheer commented on the verse saying, “It means, ‘Do not let them hear anything offensive from you, and do not even say, ‘Uff!’ which is the mildest word of disrespect.’”

Allah knows best.