This is done many times because the client is elderly and concerned about someone in the family having access to funds to pay bills if they become sick or incapacitated. This is the wrong way to do things in almost every case. We have Powers of Attorney to accomplish these purposes. An agent under a Power of Attorney has special responsibilities under the law which are known as fiduciary duties. They can not favor themselves and being an agent under a Power of Attorney is not a license to steal. Do agents sometimes do things they shouldn't do --sure. Agents are legally held to a high standard under the law.
The problem with making your child or children joint tenants is that it creates a presumption under the law that it is your intention upon your death that the joint tenant should be the sole owner of the account. If you want that account divided equally among all your children you could have big problems. A joint tenant can also go into the Bank and withdraw all of the money without your knowledge or permission. I had one client that had 3 children and added each child as a joint tenant on each of three different CDs she owned. Now if one CD needs to be cashed in to bill some medical bills who is the odd man out?
There are a number of ways to avoid probate that maybe much better than than the do it yourself method of adding your children as joint tenants. I don't want want your children's financial problems to be your financial problems. If the bill collectors are chasing your kids what makes you think they are going to stop when their research shows up that joint account with you. What about if your kids don't have enough liability coverage and manage to run over an orthopedic surgeon crossing the street in front of the hospital. When you kill someone who makes $900,000 per year in slow year it is going to get expensive. What if one of your kids decides they don't want to be married anymore? Are you going to have prove to some Court that the money in that joint account is not their's? Why in the world would want any of these worries when they could easily be avoided. Discuss your options with a well qualified Elder Law attorney. You will rest easier knowing your approaching this the appropriate way.