well you should always check with the relevant authority and not just take peoples word for it on here or anyone else who tells you something.
but who ever told you, they are wrong, i've claimed tax creds and child benefit since my wife and daughter came to the uk, and she had no problems at all getting ILR.
so stop worrying. just remember only you can claim and put it in your account
tax creds is a public fund, but there is a clause thou, where for immigration purposes its not classed as a public fund, thats the reason why you can claim it.