Quite tricky, this one. In our case my DH bought his ex gf a house, a car, and also makes regular support payments. The ex gf does not work and seems very resourceful at getting things and money from others. She does not have a regular job and has worked a total of 12 weeks in the last 5 years, plus the odd boot fair, etc. She also gets financial help from her parents and, much to our bewilderment, from DH's parents as well. In the past she has claimed benefits that she wasn't legally entitled to receive so she's quite happy to take from the "rich" taxpayers, too.
In order to be near to DSS, we have chosen to stay living in a community where we both earn far, far less than we could somewhere else and this continues to negatively affect our financial security. Our social circle is a horrible rumour mill fueled by every tiny bit of gossip and I often hear about how much she struggles for money. It was her choice to leave the relationship as she left DH for another man when DSS was 4. Despite having a myriad of boyfriends and living rent-free in other people's houses (before she finally settled on which house she wanted DH to buy for her), she is a single mother so it's not hard for her to get a lot of sympathy from others. She chooses to use the support payments to support herself as well as DSS, but that is her choice and there is nothing DH can do about it.
The difference between our households couldn't be more obvious and I often wonder how DSS (14-yrs old) perceives the difference. We are by no means wealthy and often have to make sacrifices like other families, but we manage our money well. I get the distinct impression that she and her friends see DH and I as "greedy capitalists" who won't share the wealth while she struggles for every crumb of food. What they don't see is that we both work very hard and DH has given, and continues to give, more than what is legally expected of him. He just wants to do the right thing. I do worry that DSS is not aware of how much his father provides for him. We have taken him on expensive holidays, bought him expensive gifts, always make sure he has clothing, etc. but these things are never acknowledged.
We take a similar approach to you, Elizabeth120914 in that we simply try to show that, if you work hard and use your money responsibly, you give yourself more choices and opportunities. These are individual choices, whether to live on charity and embrace a life of leisure or to work to have a nice home, travel, etc. I hate that DSS should ever have to think about whether his father gives his mother enough money, but sadly I think it's a reality of split families. :-(
Oh dear, sorry for the rant! To answer your question PlinkertyPlonk I think it is important for the kids to understand that parents are providing for them. They don't need to know details and amounts but IMO they need to know that their fathers have not abandoned their responsibilities.