In and of itself, for a Catholic to occasionally attend a Protestant church as a guest so as to please family is not a problem. What is a problem is the possibility that your wife might expect you to continue to attend a Protestant church with her and your children *as if you had never become a Catholic *(in other words, on a regular basis as a congregant, rather than occasionally as a guest).
If you become a Catholic, you must become a wholehearted Catholic – which would mean that your duties as a Catholic take precedence in your Christian life. While you cannot expect your wife to violate her conscience and leave her church to follow you when she cannot accept Catholicism as true, neither can she expect you to behave as if you had never become Catholic so as to please her. As for the children, you both entered marriage as non-Catholics, expecting to raise your children non-Catholic, so you cannot require that your children become Catholic. (Should older children decide they
want to become Catholic, that is a different matter.)
Should you decide to convert, I can only recommend sitting down with your wife and working out a compromise. Perhaps you might agree to go to her church with her and your children for important holidays (e.g., Christmas, Easter) and for religious milestones (e.g., baptisms, weddings, funerals), and occasionally “just because” (assuming, of course, that you meet your Sunday/holy day obligation by attending Mass either on the holy day or on the vigil of the preceding evening). In return, she could agree to respect your need to follow Christ in the Catholic Church. (If she and the children could occasionally attend Mass with you as a reciprocal gesture, all the better.)
Recommeded reading:
How to Become a Catholic