I was thinking about what my sister did to her 13year old son last summer which was summer military camp.. She said that its a good place to really train your child proper discipline and value responsibility at the same time.
There's lots of craft activities you can do with your kiddos, especially for these easter.. I've had lots of fun making easter eggs and easter baskets. Here's some fun marbelized eggs:
and easter baskets:
A stroll at the park in the morning is a good idea. You can take them to a museum or have a little camping in the back yard/front yard of your home. If you have a mini-size pool, they can play and swim in the water along with your assistance.
I'd recommend getting your son into a sport or activity that he likes and most importantly make sure he's with a buddy or two. As for your 5 year old you should also get her with some friends and set up play dates and potentially a sport or activity that she likes, you'll be able to bring your 12 month old with you as long as they're occupied. If one of your older kids is not occupied you should have one-on-one-one time with them and your youngling. You can teach them how to care for him and instill the wanting to be a role model and good older sibling.