What should I put on my toddlers spider/ant bites?

Calamine Lotion. Calamine lotion should work well to relieve itching and soreness until the bites heal.
Otc. Usually for a simple insect bite, otc Hydrocortisone 1% cream or Benadryl (diphenhydramine) cream helps relieve the redness and itching. If it starts bleeding, swelling or crusting, it's advised to see your doctor.