No the mother absolutely does not need to send money. The kids have their father to help them buy extras if they want. If you feel oh so obligated to only give so much, take half of the babies "budget" and give it to them. He absolutely, 100% does NOT need it and would be perfectly happy with a small stuffed whatever and call it a day. TRUST ME. I have a few kids myself and all have been under 2 that have been to Disney and they couldn't have cared less and don't remember it at all to this day so it will be okay to not be "fair" with spending money, he won't remember that when he is um 3? 
I am a step kid and this thread really saddens me with the resentment towards these kids you have. Even if you spend more time with them, that certainly doesn't take the resentment away.

I am a step kid and this thread really saddens me with the resentment towards these kids you have. Even if you spend more time with them, that certainly doesn't take the resentment away.