Praise be to Allah.
Practising sports of various kinds that do not go against the rulings of sharee’ah and that fulfil the aim of worshipping Allaah is one of the things that are encouraged by Islam, so as to attain physical strength and mental health. The evidence of the Qur’aan and Sunnah indicates that this is allowed in sharee’ah and is in fact encouraged.
But in some cases these sports may be haraam, not in and of themselves, but because they include some haraam things. This applies to what you have mentioned in your question.
An example of the haraam things that may happen is bowing to someone other than Allaah. It was narrated that Anas ibn Maalik (may Allaah be pleased with him) said: “A man said, ‘O Messenger of Allaah, when one of us meets his friend, can he bow to him?’ The Messenger of Allaah (peace and blessings of Allaah be upon him) said, ‘No.’ He said, ‘Can he hug him and kiss him?’ He said, ‘No.’ He said, ‘Can he shake hands with him?’ He said, ‘Yes, if he wishes.’” (Narrated by al-Tirmidhi, 2728; he said it is a hasan hadeeth. Also narrated by Ibn Maajah. 3702. The hadeeth was classed as hasan by al-Albaani in al-Silsilah al-Saheehah, 160).
Ibn Taymiyah said: “With regard to bowing in greeting, this is forbidden as narrated in al-Tirmidhi from the Prophet (peace and blessings of Allaah be upon him), that they asked him about a man who meets his brother and bows to him, and he said no to that. That is because it is not permitted to bow or prostrate for anyone except Allaah.” (Majmoo’ al-Fataawa, 1/377).
If you know that the person whom you invite to join will do something haraam or something that is a kind of shirk, then you should not do that, whether the one whom you invite is a child or an adult, because that is a kind of cooperating in sin, and Allaah says (interpretation of the meaning):
“Help you one another in Al‑Birr and At‑Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression”
May Allaah help us and you to do that which He loves and which pleases Him. May Allaah send blessings and peace upon our Prophet Muhammad and his family and companions.